OPR-J377-KR-15 Approaches to Breton Sound, LA Gulf of Mexico Ocean Surveys, Inc. H12735 3 5 NM East of Mississippi River-Gulf Outlet Louisiana United States 20000 2015 George G. Reynolds Navigable Area 2015-04-23 2015-06-18 2015-07-28 Multibeam Echosounder Side Scan Sonar Multibeam Echosounder Backscatter meters Universal Transverse Mercator (UTM) UTC Atlantic Hydrographic Branch The purpose of this survey is to update existing NOS nautical charts in a high commercial traffic area. All times are recorded in UTC. Data recorded and presented relative to UTM Zone 16 North. THE INFORMATION PRESENTED IN THIS REPORT AND THE ACCOMPANYING BASE SURFACES REPRESENTS THE RESULTS OF SURVEYS PERFORMED BY OCEAN SURVEYS, INC. DURING THE PERIOD OF 18 JUNE TO 28 JULY 2015 AND CAN ONLY BE CONSIDERED AS INDICATING THE CONDITIONS EXISTING AT THAT TIME. REUSE OF THIS INFORMATION BY CLIENT OR OTHERS BEYOND THE SPECIFIC SCOPE OF WORK FOR WHICH IT WAS ACQUIRED SHALL BE AT THE SOLE RISK OF THE USER AND WITHOUT LIABILITY TO OSI. Contractor This survey provides hydrographic data for the Gulf of Mexico waters at the entrance to the Mississippi River-Gulf Outlet. The general locations of the survey limits are presented in Table 1. 29.4420694444 88.9880972222 29.2991666667 88.9019444444 Survey limits were acquired in accordance with the requirements in the Project Instructions and the HSSD. The purpose of this survey is to provide NOAA with accurate hydrographic data to update existing National Ocean Service (NOS) nautical charts in a high commercial traffic area located in the Gulf of Mexico east of the Mississippi River delta. The survey area includes multiple offshore platforms and pipelines. The entire survey is adequate to supersede previous data. Survey Coverage is in accordance with the requirements in the Hydrographic Survey Project Instructions (April 23, 2015), the Statement of Work, 2015 (SOW), and the Hydrographic Specifications and Deliverables, April 2014 (HSSD). In all waters shallower than 20 meters, one hundred percent (100%) side scan sonar (SSS) coverage with concurrent multibeam echosounder (MBES) with backscatter coverage were collected with set line spacing. In waters 20 meters and deeper, Complete Mulitbeam with backscatter coverage was acquired. Additional SSS and MBES coverage was obtained as necessary to fill gaps in coverage, to provide a least depth for all significant SSS contacts and for charted feature disprovals. Gaps in the 100% SSS coverage were addressed with SSS fill-in lines or covered with complete MBES data. The final survey area covers 30.28 square nautical miles (Figure 1). Survey H12735 MBES coverage overlaid on RNC 11366. H12735_Figure_1_Coverage.jpg R/V Ocean Explorer 0 358.37 0 0 0 359.73 0 48.36 0 0 361.15 0 0 0 356.94 0 48.36 0 7.08 8 0 0 0 0 30.28 2015-06-19 2015-06-20 2015-06-25 2015-06-26 2015-06-27 2015-06-28 2015-07-02 2015-07-04 2015-07-09 2015-07-10 2015-07-11 2015-07-12 2015-07-14 2015-07-15 2015-07-21 2015-07-22 2015-07-26 2015-07-28 The lineal nautical miles (LNM) for MBES only development lines were included under the heading "Mainscheme MBES" along with the LNM for the Complete Multibeam mainscheme lines in Table 2. Hydrographic Survey Statistics. Refer to the OPR-J377-KR-15 Data Acquisition and Processing Report (DAPR) for a complete description of data acquisition and processing systems, survey vessels, quality control procedures and data processing methods. Additional information to supplement sounding and survey data, and any deviations from the DAPR are discussed in the following sections. R/V Ocean Explorer 18 2 Survey operations were conducted from the R/V Ocean Explorer. The R/V Ocean Explorer, O.N. 905425, is an 18-meter aluminum vessel, with a 5.1-meter beam and nominally 2-meter draft, powered by two 1,000 HP Iveco diesel engines. Reson 7125 MBES EdgeTech 4200 SSS ODIM MVP30 w/AML SVPT Sound Speed System AML Micro-X Sound Speed System Applanix POS MV 320 V.4 Positioning and Attitude System Trimble MS750 Positioning System Trimble ProBeacon Positioning System Table 5 summarizes the primary equipment used to acquire MBES and SSS data. All equipment was installed, calibrated and operated in accordance with the DAPR. A total of 48.36 nm of cross line data were acquired June 19 to June 20, and July 26, 2015 (DN 170 - 171, DN 207). Per the 2014 HSSD, the cross line requirements were dependent on coverage type. For "Set Line Spacing" coverage areas, the lineal mileage of cross lines shall be a minimum of 8% of main scheme MBES mileage. For "Complete Multibeam" coverage, the lineal mileage of cross lines shall be a minimum of 4% of mainscheme MBES mileage. The survey area H12735 was divided approximately 50/50 between Set Line Spacing coverage and Complete Multibeam coverage, with the 20-meter depth curve traversing diagonally across the center of the survey area. Cross lines were run nominally perpendicular to mainscheme lines (Figure 2). Approximately 32.0 nm of cross lines intersected the 359.73 nm of mainscheme MBES lines acquired to meet the Set Line Spacing coverage requirements, with cross line mileage equaling 8.9% of mainscheme mileage. Approximately 21.9 nm of cross lines intersected the 323.22 nm of mainscheme MBES lines acquired to meet the Complete Multibeam coverage requirements, with cross line mileage equaling 6.8 % of mainscheme mileage. Cross line mileage for the entire survey area equaled 7.1% of the total 682.95 nm of mainscheme MBES lines. Soundings from mainscheme lines and cross lines were compared periodically throughout survey operations reviewing preliminary MBES surfaces and using CARIS HIPS Subset Editor. Cross line comparisons provided confirmation that the system offsets and biases were entered correctly and verified the accuracy of sounding correctors (i.e. tide, sound speed, TrueHeave). Statistical quality control information was compiled from a difference surface, generated in CARIS HIPS, between the depth layer of a 2-meter CUBE (Combined Uncertainty and Bathymetric Estimator) surface composed only of cross line data and the depth layer of a 2-meter CUBE surface composed only of mainscheme MBES data. The cross line analysis results demonstrate excellent agreement between cross line soundings and mainscheme soundings, with the depth differences less than or equal to 0.42 meters. The allowable TVU for the range of water depths within Survey H12735 is greater than 0.50 meters. Figure 3 is a histogram showing the distribution of depth differences for all comparison grid cells considered. The total number of 2-meter comparison cells equaled 1,349,427. Of 1,349,427 possible comparison cells, 1,347,641 or 99.87% of the cells include cross line and mainscheme soundings that match within +/- 20 centimeters. An overview of the cross line layout on a 2-meter surface created from mainscheme MBES data and colored by depth. The surveyed 20-meter depth curve is represented by the red contour line with the tracklines colored in black. RNCs 11363 and 11361 are visible in the background. H12735_Figure_2_XL.jpg The graph shows a frequency distribution of the depth differences between the H12735 cross line data and the H12735 mainscheme MBES data. Statistics from the depth difference sample set are displayed above the graph. H12735_Figure_3_XL_Histogram.jpg 0.01 0.14 R/V Ocean Explorer 2 2 The methods used to minimize the uncertainty in the corrections to echo soundings are described in detail in Section B. Processing and Quality Control of the project DAPR. Survey H12735 did not deviate from the methods documented in the DAPR. The Total Vertical Uncertainty Quality Check (TVU QC) "Ratio Method" was used to evaluate IHO uncertainty for all finalized surfaces. The TVU QC "Ratio Method" is described in the Chapter 4 Appendices of the NOAA OCS Field Procedures Manual (FPM) dated April 2014. Per the FPM TVU QC section, "The hydrographer should use the finalized surface because this surface will identify areas where either the uncertainty or the standard deviation exceeded the maximum allowable error and the greater of these two values is used in addition to having the uncertainty scaled to a 95% CI, whereas unfinalized surface uncertainties are reported at the 68% CI." The FPM TVU QC section also states that, "[ratio] values which do not require further examination are from -1 to 0 and the values which do require further examination are from -100 to -1." Finalized surfaces were used in this analysis. Surfaces were finalized using the “uncertainty” option as the basis for calculating “Final Uncertainty” in the CARIS “Finalize Base Surface” utility. Eight (8) MBES CUBE surfaces were delivered along with Survey H12735 including two (2) mainscheme-specific surfaces: "H12735_MB_4m_MLLW_Final" and "H12735_MB_2m_MLLW_Final." Six (6) 50-centimeter item investigation surfaces were also delivered. The 4-meter and 2-meter surfaces are intended to satisfy coverage and sounding density requirements for Set Line Spacing and Complete Multibeam coverage areas respectively. The remaining six (6) 50-centimeter surfaces are intended to satisfy the sounding density requirements for item investigations. Results from the TVU QC indicate that 100% of the nodes from all submitted surfaces meet IHO Order 1 uncertainty specifications, i.e. the ratio values of all nodes is less than -1. The maximum ratio range of all comparison cells from all submitted surfaces is -0.48 to -0.72. Two (2) prior surveys and two (2) contemporary surveys junction with Survey H12735. Figure 4 displays the location of the prior and contemporary junction surveys for Project OPR-J337-KR-15. Survey junctions for Project OPR-J377-KR-15. RNC 11366 is displayed in the background. H12735_Figure_4_Junctions.jpg D00142 40000 2008 Terrasond, Ltd. W Terrasond, Ltd.'s Survey D00142, a reconnaissance survey conducted in 2008, overlapped the western side of the H12735 survey area. Survey D00142 was acquired with a Singlebeam Echosounder (SBES), so the junction area between the two surveys was sparse. Depth data for Survey D00142 were downloaded from the National Geophysical Data Center (NGDC) website (http://www.ngdc.noaa.gov) in the form of a 5-meter resolution Bathymetric Attributed Grid (BAG), "D00142_5m_MLLW_1of1." To conduct the junction comparison a finalized 5-meter CUBE surface was generated from the entire MBES data set for survey H12735, "H12735_MB_5m_MLLW." In CARIS HIPS, depths from the "D00142_5m_MLLW_1of1" BAG were subtracted from the depths in the "H12735_MB_5m_MLLW" CUBE surface using the CARIS HIPS Difference Surface function. A histogram of the differences is shown in Figure 5. Depths from the H12735 survey show decent agreement with depths from the D00142 survey. Depth discrepancies generally equaled 70 centimeters or less with a mean difference of -25 centimeters. On average, Survey D00142 depths were deeper than H12735 depths, which may be due to sedimentation and/or sediment transport in the H12735 survey area since the 2008 Terrasond Reconnaissance Surveys were conducted. Some of the largest discrepancies between survey depths, up to 1.29 meters, were located in the deeper southern waters of the H12735 survey area, where natural changes to the bathymetry and location of seafloor depressions and ridges have occurred between 2008 and 2015. Figure 6 highlights two of the areas where differences greater than 1 meter were observed in the CARIS Difference Surface. Additional factors that may account for the approximately 0 to 1 meter (0 to 3 feet) differences between the 2008 and 2015 surveys include the comparison of singlebeam and multibeam data, degraded horizontal accuracy associated with DGPS positioning (used for both surveys), slight misalignments between the surface grid nodes, and the use of different tide stations for tide correctors (multiple stations were used for D00142, including Pilots Station East, LA, Gulfport Harbor, MS, 874-5557, and one supplemental gauge: Olga Compressor Station, LA, 876-0889). Surface-to-surface difference histogram comparing Survey H12735 to Survey D00142. H12735_Figure_5_Histogram_D00142.jpg The difference surface generated from subtracting survey depths from D00142 from H12735 survey depths is displayed in comparison to a H12735 2-meter CUBE surface colored by depth. Two sections of the difference surface are highlighted where depth discrepancies between the two surveys exceeded 60 centimeters, with blue representing a positive difference (deepening) and green, yellow and red representing a negative difference (shoaling). Changes in bathymetry, i.e. the position of depressions associated with seafloor topography, were responsible for the largest depth discrepancies between Surveys H12735 and D00142. H12735_Figure_6_D00142_Discrepancies.jpg F00546 20000 2007 C & C Technologies, Inc. NE C & C Technologies, Inc. survey F00546, a hydrographic survey conducted in 2007 to investigate twelve (12) AWOIS items located within the Louisiana Safety Fairway, consisted of two oval-shaped survey areas surrounded by H12735 survey data. Given that the majority of the overlapping MBES data for Survey F00546 and Survey H12735 were acquired with Set Line Spacing coverage, the junction area between the two surveys was patchy. Depth data for Survey F00546 were downloaded from the NGDC website in the form of a 2-meter resolution BAG, "F00546_2m_MLLW_1of1." To conduct the junction comparison a finalized 2-meter CUBE surface was generated from the entire MBES data set for survey H12735, "H12735_MB_2m_MLLW." In CARIS HIPS, depths from the "F00546_2m_MLLW_1of1" BAG were subtracted from the depths in the "H12735_MB_2m_MLLW" CUBE surface using the CARIS HIPS Difference Surface function. A histogram of the differences is shown in Figure 7. Depths from the H17235 survey show decent agreement with depths from the F00546 survey. Depth discrepancies generally equaled 80 centimeters or less with a mean difference of -13 centimeters. On average, Survey F00546 depths were deeper than H12735 depths, which may be due to sedimentation and/or sediment transport in the H12735 survey area since the 2007 C & C survey was conducted. Some of the largest discrepancies between survey depths, up to 84 centimeters, were located where natural changes to the bathymetry and location of seafloor depressions and ridges have occurred between 2007 and 2015. Figure 8 highlights three of the areas where differences greater than +/- 50 centimeters were observed in the CARIS Difference Surface. Additional factors that may account for the differences between the 2007 and 2015 surveys include degraded horizontal accuracy associated with DGPS positioning (used for both surveys), slight misalignments between the surface grid nodes, and the use of different tide stations for tide correctors (Survey F00546 used the Gulfport Harbor, MS station, 874-5557). Surface-to-surface difference histogram comparing Survey H12735 to Survey F00546. H12735_Figure_7_Histogram_F00546.jpg The difference surface generated from subtracting survey depths from F00546 from H12735 survey depths is displayed in comparison to a H12735 2-meter CUBE surface colored by depth. Several sections of the difference surface are highlighted where depth discrepancies between the two surveys exceeded 50 centimeters, with cyan and blue representing a positive difference (deepening) and orange and red representing a negative difference (shoaling). Changes in bathymetry, i.e. the position of depressions associated with seafloor topography, were responsible for the largest depth discrepancies between surveys H12735 and F00546. H12735_Figure_8_F00546_Discrepancies.jpg H12734 20000 2015 Ocean Surveys, Inc. W The horizontal overlap between the bathymetric data from contemporary Surveys H12735 and H12736 varied between approximately 5 and 500 meters. Given that the majority of the overlap between the two surveys was in Set Line Spacing coverage collection areas, the junction area between the two surveys was patchy. Depths from 2-meter BASE surfaces compiled from the MBES data from each survey, "H12735_MB_2m_MLLW" and "H12734_MB_2m_MLLW," were compared using the CARIS HIPS Difference Surface function. A histogram of the differences is shown in Figure 9. Depths from the H12735 survey show good agreement with the depths from the H12734 survey. Depth discrepancies generally equaled 29 centimeters or less with a mean difference of 1 centimeter. Surface-to-surface difference histogram comparing Survey H12735 to Survey H12734. H12735_Figure_9_Histogram_H12734.jpg H12736 40000 2015 Ocean Surveys, Inc. E The horizontal overlap between the bathymetric data from contemporary Surveys H12735 and H12734 varied between approximately 50 and 500 meters. Depths from 2-meter BASE surfaces compiled from the MBES data from each survey, "H12735_MB_2m_MLLW" and "H12736_MB_2m_MLLW," were compared using the CARIS HIPS Difference Surface function. A histogram of the differences is shown in Figure 10. Depths from the H12735 survey show good agreement with the depths from the H12736 survey. Depth discrepancies generally equaled 20 centimeters or less with a mean difference of 5 centimeters. Surface-to-surface difference histogram comparing Survey H12735 to Survey H12736. H12735_Figure_10_Histogram_H12736.jpg Sonar system quality control checks were conducted as detailed in the Quality Control section of the DAPR. Results from the weekly MBES bar checks are included in Appendix II of the DAPR. MBES "Blowouts" The Reson 7125 system experienced periodic bursts of motion-induced noise or “blowouts,” typically affecting between 1 and 4 sequential profiles. Efforts were made to reduce this noise during acquisition, including adjustments to system gain and power, in addition to the multibeam pole fairing that was installed to reduce cavitation effects. The frequency of the noise bursts would typically increase as sea state worsened. Therefore, operations were suspended when the frequency or length of blowouts became too high. Accepted data effected by blowouts did not show any nadir gaps in coverage in excess of 3 nodes in the along-track direction. MBES Outer Beam Irregularity At times of extreme variability in surface sound speed, the MBES profiles of the Reson 7125 showed an irregularity in the outer beam data that simulated the expected signature of a roll error. It is not uncommon to see a “smile” or “frown” in a multibeam profile if the water column sound speed profile is not properly acquired or applied. In this case, the profile appears convex on the port side and concave on the starboard side thereby mimicking a roll bias. Regular and frequent roll patch testing confirmed that the multibeam mounting apparatus was stable, i.e. there was not an intermittent roll error in the system. Based on review of past Reson 7125 datasets, OSI is led to conclude that this phenomenon is either a Reson 7k system limitation or a site limitation of surveying in the freshwater plume of the Mississippi River that no sounding system could be expected to overcome. An example of the Reson 7125 "S-shape" anomaly sounding system error is shown in Figure 11. The top image is an example of the Reson 7125 S-shaped outer beam sounding irregularity (green line) which was observed on DN185, a day with highly variable surface sound speed. The bottom image shows a time series of the surface sound speed values for four of the lines collected on DN 185. Depths and distances are in meters. H12735_Figure_11_MBES_Irregularity.jpg Water Column and Surface Sound Speed Variability The sound speed profiles measured throughout the limits of the survey area showed high variability, particularly near the surface (Figure 12). A drastic change in sound speed was often observed near the surface, where sound speed values would change by over 10 m/s in the top 5 meters of the water column. At times the high sound speed variability near the surface adversely affected the depth and positioning of outer beam soundings (Figure 13). Sound speed changes in the water column were time and space dependent and appear to be attributed to the influx of fresh water from the Mississippi River and the temperature changes throughout the day. To ensure that compromised data were not included in the final surface, outer range swath trimming was effected, as needed, on a case-by-case basis. The image above represents all H12735 sound speed profiles colored by cast time of day. The profiles showed high variability in sound speed measurements spatially and temporally, with the change most pronounced near the surface. H12735_Figure_12_SVP_Profiles.jpg The top image highlights a Reson 7125 line with the outerbeams showing a "thickening " indicative of a sound speed error; rejected soundings are colored grey. The bottom image shows a sound speed profile taken with the MVP on June 27, 2015 (DN 178), that was applied to the orange line in the top image. The sound speed value increases by 12 m/s in the top 5 meters of water. Depths and distances are in meters. H12735_Figure_13_SOS_Variability.jpg SSS Refraction The dynamic sound speed changes affected the SSS imagery at times, causing refraction in the outer ranges of the SSS swath (Figure 14). When practical, to lessen the impact of refraction, the EdgeTech 4200 tow fish was flown below the refractive sound speed lens. To ensure that 100% coverage of high quality SSS data was acquired, SSS lines with excessive refraction were rejected or the portion of the line with severe refraction was re-run. Examples of refraction in the 4200 SSS imagery as it appeared in the CARIS Side Scan Editor waterfall window. H12735_Figure_14_SSS_Refraction.jpg Tide Offset Review of surface data indicated that there were several lines with tide-related offsets between MBES data collected on different days within Survey H12735. However, there were no noteworthy tide events that affected this survey. Overall, the tide correctors were modeled well for Survey H12735, showing good agreement between survey days. Tide offsets generally equaled 12 centimeters or less and are likely associated with local environmental effects, i.e. wind setup. An example of a tide related offset noted in Survey H12735 is presented in Figure 15. The left image shows a subset window displayed over the Standard Deviation layer from a H12735 2-meter CUBE surface. The cyan color highlights areas of higher standard deviation in the surface due to a tide offset. On the right, MBES data loaded into CARIS Subset Editor shows the tide-related vertical offset between cross line soundings collected on DN 171 (teal) and mainscheme soundings collected on DN 177 (green). Depths and distances are in meters. H12735_Figure_15_Tide_Offset.jpg Sea Surface Noise in SSS Imagery There were occasional wakes recorded in the side scan imagery from vessel traffic associated with commercial fishing and oil field support vessels. The wakes were noted in the acquisition and processing logs. When a large wake was identified in the coverage mosaic, the coverage gap was filled with SSS or MBES development lines. In addition to vessel wakes, the towed 4200 SSS occasionally recorded reflections off of the surface, including sea squall noise, seaweed, and large balls of fish located above the tow fish in the water column. The surface noise appeared as shadowless dark spots in the SSS imagery (Figure 16). Lines that were affected by surface noise were carefully scrutinized to ensure all possible SSS contacts were selected. The top image is an example of surface noise recorded during a rain squall and the bottom image shows reflections off of fish on the sea surface or in the water column above the towed SSS. Both images were taken in the CARIS Side Scan Editor waterfall window. H12735_Figure_16_Surface_Noise.jpg Fish in SSS Imagery and MBES data An abundance of fish and marine sea life were seen in the SSS and MBES data, either as lone swimmers or in schools (Figures 17 - 18). Fish and dolphins were noted in the acquisition log by the field team, and these areas were carefully reviewed during data processing. Shadows in the SSS, usually detached from a dark return, were typically associated with fish either in the water column or at a position closer to nadir. In the cases where a visible shadow was recorded in the SSS, the contact was designated as a fish, for two reasons: 1) the possibility that the assumed fish was actually a feature and 2) to assist processors in rejecting fish-related noise from the MBES data. Dolphin pods were a persistent presence within the survey area, as well as large schools of fish, which at times created large shadows in the SSS imagery and gaps in the MBES data where fish and dolphins were rejected (Figure 19). To ensure that possible significant features were not located in these fish and dolphin shadows, these fish/dolphin related coverage gaps were developed with object detection MBES coverage. The top images are screen grabs of MBES data loaded into the CARIS Subset Editor 3D (left) and 2D (right) windows that show a school of fish near the seafloor that has been rejected from the data (grey soundings). The bottom image shows the same school of fish as recorded in the SSS imagery. H12735_Figure_17_Fish_SSS-MB.jpg Examples of fish schools and lone swimmers as they appear in several subsets of the side scan imagery captured in CARIS Side Scan Editor's waterfall window. Two of the screen grabs display the raw, un-slant range corrected imagery to show the fish returns in the water column with their detached shadows. Two of the screen grabs are of slant-range corrected and AVG corrected SSS lines; therefore, the water column is not visible. H12735_Figure_18_Fish_SSS.jpg The top image shows a pod of dolphins as it was ensonified with the Reson 7125, and the bottom image shows the same dolphins as captured in the SSS imagery. The dolphins produced shadows in both sonar coverages. H12735_Figure_19_Dolphins.jpg Sound speed measurements were acquired and processed as documented in the DAPR. All MBES lines were sound speed corrected using CARIS HIPS’ “Nearest in Distance Within Time” method with the time set to two (2) hours. This survey was conducted to develop 100% SSS coverage along with concurrent MBES with backscatter to a depth of 20 meters, i.e. Set Line Spacing coverage as defined in Section 5.2.2.3 of the HSSD. In depths over 20 meters, Complete MBES coverage with backscatter was acquired. There was one gap in the 100% side scan coverage mosaic within the survey limits for H12735. The gap located at 29-24-01.75 N, 88-58-10.70 W occurred where the survey vessel deviated from the line plan to maneuver safely around a large offshore platform. The survey vessel was unable to completely cover the SSS gap with MBES coverage due to the limitations of safe navigation around the large platform; the MBES system could not completely ensonify the seafloor between the three-towered platform. Per the OPR-J377-KR-15 Project Instructions which stated "Gaps in SSS coverage should be treated as gaps in MBES coverage and addressed accordingly," gaps in SSS coverage and holidays caused by fish, dolphins, or boat wakes were developed with Complete Multibeam coverage. This methodology was confirmed with OSI's NOS Contracting Officer (COR) through an email correspondence dated July 21, 2015. Text from the emails discussing SSS holidays are included in the DR Appendix II, Supplemental Survey Records and Correspondence. All potentially significant features located with mainscheme SSS or MBES were developed with high density multibeam sonar data to meet the HSSD requirement for “Object Detection" coverage. The survey methods used to meet coverage requirements did not deviate from those described in the DAPR. Density To confirm the HSSD coverage requirement that at least 95% of the surface nodes shall be populated with at least 5 soundings for Complete Multibeam and Object Detection coverage surfaces and at least 3 soundings for Set Line Spacing coverage surfaces, the Compute Statistics tool was utilized within CARIS HIPS and SIPS to generate statistics for the Density layer for each finalized BASE surface. For the purpose of obtaining the most accurate surface density statistics, the surfaces used for the Density QC check were finalized with the "Apply Designated Soundings" box unchecked, as it was discovered that when this option was selected during surface finalization a density value of one (1) was assigned to all nodes containing a designated sounding, regardless of the node's sounding density value pre-finalization. That said, all MBES coverage surfaces included with the survey deliverables were re-finalized with the "Apply Designated Soundings" option selected. The Compute Statistics tool generates an ASCII export containing two columns: 1) sounding density value and 2) the number of nodes that returned that value. This export was used to determine the percentage of nodes with a sounding density ≥ 5 for every Complete Multibeam and Object Detection coverage CUBE surface and the percentage of nodes with a sounding density ≥ 3 for the Set Line Spacing coverage CUBE surface. The percentage of nodes with density greater than or equal to 3 soundings for the Set Line Spacing coverage surface was as follows: H12735_MB_4m_MLLW_Final = 99.92%. The percentage of nodes with density greater than or equal to 5 soundings for the Complete Multibeam coverage surface was as follows: H12735_MB_2m_MLLW_Final = 99.94%. Five (5) of the six (6) Object Detection surfaces had 100% of the nodes populated with a density greater than or equal to 5 soundings. The percentage of nodes with density greater than or equal to 5 soundings for surface H12735_MB_50cm_MLLW_C-054_Final was 99.97%. All data reduction procedures conform to those detailed in the DAPR. System calibrations were performed as documented in Section C. of the DAPR. The initial MBES system calibration, or patch test, was performed on June 18, 2015 (DN 169). On July 5, 2015 (DN 186) the draft of the Reson 7125 transducer was deepened. A new calibration was performed after lowering the transducer draft. Reson 7125 Patch Test 2015-07-05 Change in transducer draft. Backscatter data were acquired concurrent with bathymetry data for Survey H12735. Per the Hydrographic Survey Project Instructions, MBES bathymetry was the priority on this project; therefore, the multibeam system settings were optimized for acquisition of bathymetry. Backscatter data were recorded with HYSWEEP SURVEY in .7K format. These data were periodically reviewed to ensure function of the backscatter acquisition process. However, per the Project Instructions, OSI was not required to “process or create any additional backscatter products.” As such, these data are delivered in raw format in the “Backscatter” directory. NOAA Extended Attribute object catalogue V 5.3.2. Software versions described in Section A of the DAPR were used throughout acquisition and processing of data for Project OPR-J377-KR-15. H12735_MB_4m_MLLW_Final CUBE 4 11.17 20 NOAA_4m Set Line Spacing Coverage H12735_MB_2m_MLLW_Final CUBE 2 18 34.12 NOAA_2m Complete MBES H12735_MB_50cm_MLLW_C-003_Final CUBE 0.5 11.17 20.71 NOAA_0.5m Object Detection H12735_MB_50cm_MLLW_C-016_Final CUBE 0.5 14.36 17.21 NOAA_0.5m Object Detection H12735_MB_50cm_MLLW_C-026_Final CUBE 0.5 14.72 17.79 NOAA_0.5m Object Detection H12735_MB_50cm_MLLW_C-052_Final CUBE 0.5 15.46 18.70 NOAA_0.5m Object Detection H12735_MB_50cm_MLLW_C-053_Final CUBE 0.5 16.23 18.04 NOAA_0.5m Object Detection H12735_MB_50cm_MLLW_C-054_Final CUBE 0.5 17.06 17.98 NOAA_0.5m Object Detection H12735_SSS_100 SSS Mosaic GeoTiff 1 N/A 100% SSS Eight (8) MBES CUBE surfaces and one (1) SSS mosaic comprise the total surfaces delivered with Survey H12735. To demonstrate MBES coverage requirements were met for Set Line Spacing, a 4-meter CUBE surface was generated for the entire survey area and finalized according to depth, with a depth range of 0 to 20 meters. To satisfy the MBES coverage requirement of Complete Multibeam coverage in depths over 20 meters, a 2-meter CUBE surface was generated for the entire survey area and then finalized according to depth such that the minimum depth range for the finalized 2-meter surface was 18 meters, per Section 5.2.2.2 in the HSSD. Six (6) small field sheets were generated over significant features and populated with 50-centimeter CUBE surfaces to demonstrate Object Detection coverage. A 1-meter SSS mosaic was submitted as a GeoTIFF to satisfy the SSS coverage requirements of 100% coverage. In addition, a higher resolution, 25-centimeter SSS mosaic image composed of all SSS lines was submitted in the ECW (Enhanced Compressed Wavelet) format to assist with the survey review. Additional information discussing the vertical or horizontal control for this survey can be found in the accompanying Horizontal and Vertical Control Report (HVCR) for Project OPR-J377-KR-15. Mean Lower Low Water Discrete Zoning Pilots Station East, SW Pass, LA 876-0922 8760922.tid Final Approved J377KR2015RevCORP.zdf Final A final verified tide file was created from verified tide data obtained from the CO-OPS website upon completion of survey operations. As documented in the HVCR, with CO-OPS approval OSI removed numerous short period "data spikes" from the verified tide data via application of a fourth-order, zero-lag, Butterworth low-pass filter. The source of the abundant data spikes is suspected to be wakes from passing ships as they enter Southwest Pass. Discrete zoning methods were utilized to apply tide correctors in CARIS HIPS and SIPS. The survey area is located within Zones CGM125, CGM123, CGM124, CGM119, CGM115, CGM119, and CGM228 as provided in the preliminary tidal zoning scheme included with the project SOW. Based on the results of cross line analysis, the time and range factors as provided in the preliminary zoning scheme were adequate. Preliminary zoning, provided by CO-OPS, was accepted as the final zoning for Project OPR-J337-KR-15. North American Datum of 1983 (NAD83) UTM Zone 16 North English Turn, LA (primary), 293 kHz Eglin Air Force Base, FL (secondary), 295 kHz All data products, except the S-57 Final Feature File (FFF) are referenced to Latitude/Longitude, UTM Zone 16 North. The S-57 Final Feature File, H12735.FFF.000, is referenced to the World Geodetic System Datum of 1984 (WGS 84) as specified in Section 8.2 S-57 Format Features Deliverables of the HSSD. All MBES and SSS line and item investigation position data were acquired using an Applanix POS-MV operating in Differential GPS (DGPS) mode. The unit was configured to receive USCG Differential beacon correctors from English Turn, LA station. Differential beacon correctors from Eglin Air Force Base, FL station were used by the secondary navigation system (Trimble MS750) to facilitate real-time horizontal control confidence checks. Prior to and during the course of the survey the accuracy of the primary positioning system was verified by means of a physical measurement to one of two horizontal control points established at the vessel’s base of operation, the USCG Station in Venice, LA. Position confidence checks were accomplished, when possible, during fuel or weather stops. Refer to the DAPR and HVCR for additional details. Chart comparisons were performed in CARIS HIPS/SIPS and Notebook using finalized BASE surfaces and contours and selected soundings. The latest editions of the NOAA NOS Raster Nautical Charts (RNC) and Electronic Nautical Charts (ENC) were downloaded from the NOAA Office of Coast Survey website (http://www.nauticalcharts.noaa.gov/) weekly during survey operations, and after the survey was completed for final comparisons. The RNCs and ENCs used for final comparisons were downloaded on September 11, 2015 and are submitted with the survey deliverables. Local Notice to Mariners (LNM) and Notice to Mariners (NM) spanning the period beginning at the date of issuance of the Hydrographic Project Instructions (April 23, 2015) and ending on August 26, 2015 were consulted in conjunction with the foregoing chart comparison. The following sections adhere to the Descriptive Report sounding rounding system as described in Section 5.1.2 of the HSSD. Specifically, features described below having “precision” depths are presented in the following manner: ff feet (mm.mm meters, ±t.tt TPU) where ff = depth expressed in feet (chart units) having been rounded based on the precise meters expression of the depth using the 0.75 round value rule. mm.mm = depth expressed in meters ±t.tt = Total Propagated Uncertainty (TPU) expressed in meters An example of this notation follows: 80 feet (24.58 meters, ±0.24 TPU). During the chart comparison it was found that the least depth soundings for charted regions were on obstruction features; however, the chart comparisons documented below will discuss general seafloor changes, shoaling and deepening trends. All new or charted features identified, updated or disproved within Survey H12735 were addressed and attributed in the S-57 Final Feature File. For more information on the methodology that was used to build the FFF see Section B.2.5 Feature Verification in the DAPR. An overview of the areas of change between charted depths and H12735 surveyed soundings is shown in Figure 20. The figure displays a difference surface made by subtracting a 10-meter resolution depth surface generated from the H12735 MBES data from a 250-meter resolution depth surface interpolated from the charted ENC soundings within the project area. Regions of shoaling are represented by positive depth differences and regions of deepening are represented by negative depth differences. The greatest areas of change were a deepening trend in the center of the survey area and shoaling along the southern survey limit. A detailed description of each chart comparison follows. A depth difference surface overlaid on RNCs 11363 and 11361 provides an overview of the areas of change between charted depths and H12735 surveyed soundings. H12735_Figure_20_Chart_Comp_Diff_Surf.jpg 11353 2 40000 7 2014-03 2015-08-04 2015-08-08 There is good agreement between the surveyed and charted depths, with soundings differing by approximately 0 to 3 feet (0.9 meters). The largest discrepancy was identified at 29-22-19.50 N, 88-58-16.70 W, where surveyed soundings were 5 feet (1.5 meters) deeper than the charted 52-foot depth. There is good agreement between surveyed depths and the charted 60-foot contour that intersects the southwest section of Survey H12735. Survey depths differed by 1 to 2 feet (0.3 to 0.6 meters) from the charted 60-foot contour. The contour is delineated with a dashed line which, according to the NOAA publication U.S. Chart No. 1, indicates that it is an approximate depth contour. 11363 1 80000 44 2013-02 2015-08-04 2015-08-08 There is good agreement between the majority of surveyed and charted depths, with soundings differing by approximately 0 to 3 feet (0.9 meters). Shoaling was observed in the southwestern portion of the H12735 survey area where surveyed depths were 4 to 10 feet (1.2 to 3.0 meters) shallower than charted depths in the vicinity of 29-19-24.25 N, 88-57-42.80 W (Figure 21). However, this portion of the seafloor charted with depths of 78 and 72 feet on RNC 11363 is represented by different depth values of 70 and 66 feet on RNC 11361 (Figure 22). The depth values on RNC 11361 agree well with the H12735 surveyed depths. It is recommended that the disproved depths on RNC 11363 be updated to match those on RNC 11361. Overall surveyed depths are 1 to 4 feet (0.3 to 1.2 meters) deeper than charted depths across the center of the H12735 survey area, with the largest deepening observed over a 49-foot charted depth located at 29-24-09.55 N, 88-55-40.90 W where surveyed depths measure 54 feet (16.5 meters). The charted 60-foot contour traverses the center of the H12735 survey area. The surveyed 60-foot depth curve agrees well with the charted 60-foot contour within the western half of the H12735 survey area, but the charted and surveyed 60-foot contours begin to deviate at approximately 29-22-31.20 N, 88-56-23.50 W. At the eastern limit of Survey H12735, the surveyed 60-foot depth curve has migrated over 1 kilometer north of its charted location (Figure 23). The southwestern portion of the charted 60-foot contour that intersects with Survey H12735 is charted as a dashed line, indicating it is an approximate depth contour. Surveyed soundings colored in orange are overlaid on RNC 11363 to highlight a shoaling trend developed over charted depths of 68, 72, and 78 feet. H12735_Figure_21_RNC11363_Shoaling.jpg The two images show the same geographic subset of RNC 11363 (left) and RNC 11361 (right) that intersect the H12735 survey area. There is a noted discrepancy between the charted depths on RNC 11363 and RNC 11361, with the depths on RNC 11361 agreeing well with H12735 surveyed soundings. H12735_Figure_22_11363-11361_Discrepancy.jpg The charted 60-foot contour in the northeastern portion of the survey area has migrated north of its charted location. Survey soundings colored by depth are overlaid on RNC 11363. All depths are in feet. H12735_Figure_23_RNC11363_60ft_Ctr.jpg 11361 1 80000 78 2015-06 2015-08-04 2015-08-08 There is good agreement between the majority of the surveyed depths and the depths charted on RNC 11361, with soundings differing by 0 to 3 feet (0.9 meters). Shoaling was observed in two locations, where surveyed depths are 4 feet (1.2 meters) shallower than the charted 68-foot depth located at 29-19-42.30 N, 88-58-01.60 W and 5 feet (1.5 meters) shallower than the charted 92-foot depth located at 29-18-40.80 N, 88-55-33.20 W. The surveyed depths agree well with the small section of the RNC 11361 60-foot contour that intersects Survey H12735, an approximate depth contour. US5LA24M 40000 39 2014-09-19 2015-09-09 true RNC 11353 is the source for ENC US5LA24M; therefore, the positions and values of the soundings and contours included in ENC US5LA24M are identical to those charted on RNC 11353. All chart comparison notes entered under the RNC 11353 section apply to US5LA24M. US4LA33M 80000 27 2013-08-21 2015-09-09 true RNC 11361 is the source for ENC US4LA33M; therefore, the positions and values of the soundings included in ENC US4LA33M that coincide with H12735 are identical to those charted on RNC 11361. All chart comparison notes entered under the RNC 11361 section apply to US4LA33M. US4LA34M 80000 29 2015-01-06 2015-09-16 true RNC 11363 is the source for ENC US4LA34M; however, the southern extent of RNC 11363 extends over 3 kilometers south of the southern extent of US4LA34M. The positions and values of the soundings included in ENC US5LA34M that coincide with H12735 are identical to those charted on RNC 11363. All chart comparison notes entered under the RNC 11363 section apply to US4LA34M, except for the instance of shoaling and mis-matched soundings that occurred on RNC 11363 south of the southern limits of ENC US4LA34M. No AWOIS items were assigned for this survey. No Maritime Boundary Points were assigned for this survey. Two (2) position approximate (PA) charted obstructions positioned at 29-24-42.07 N, 88-58-35.74 W and 29-23-53.33 N, 88-57-46.12 W were assigned for investigation within the Composite Source File (CSF) provided with the OPR-J377-KR-15 Project Instructions. Both obstructions were disproved with 100% SSS coverage and complete MBES coverage within the search areas defined by 160-meter radii centered on each feature. No uncharted features from miscellaneous sources were provided for investigation for Survey H12735. However, two new obstructions were identified within the survey area and are included in the H12735 S-57 FFF. 3 H12735_DtoN_1.000 2015-07-10 H12735_DtoN_2.000 2015-09-11 H12735_DtoN_3.000 2015-10-09 Three (3) Danger to Navigation (DtoN) S-57 files (.000) were submitted to the Atlantic Hydrographic Branch (AHB) for Survey H12735. The DtoN #1 submission included a new 30-foot (9-meter) tall obstruction located at 29-20-20.70 N, 88-57-46.74 W that was added to RNC 11363 and 11361 as a 36-foot obstruction on July 23, 2015. The 36-foot obstruction has yet to be added to ENC US4LA33M. All features submitted with H12735 DtoNs #2 and #3 were possible exposed pipelines. A total of forty-three (43) possible exposed pipeline features were submitted as DtoNs following guidance found in Section 8.1.3 of the 2014 HSSD which states that "Dangers to Navigation shall be recommended for," among other things, "Exposed or leaking submerged pipelines." AHB chose not to submit the pipeline DtoNs to the Marine Chart Division. AHB's reasoning, shared with OSI in an email pertaining to contemporary Survey H12734 DtoN #1 and sent on July 29, 2015, holds true for all pipeline features within the project area. The email states, "AHB will not be submitting these features to Nautical Data Branch and Marine Chart Division based upon the fact it does appear to be elevated pipelines and the location is on and/or near charted pipelines. The charted pipelines are linear obstructions and the chart includes a note to exercise caution in pipeline areas." AHB submitted the reported features to NOAA's Central Gulf Coast Navigation Manager Tim Osborn such that the information could be relayed to the proper authorities. The DtoNs are included in the H12735 S-57 Final Feature File, H12735.FFF.000. Danger to Navigation Reports as well as correspondence regarding the DtoN submissions are included in Appendix II of this report. A Caution Area (CTNARE) encompasses all the affected charts within the OPR-J377-KR-15 project area. The CTNARE's Information field states: "Uncharted platforms, gas and oil well structures, pipes, piles and stakes can exist within the limits of this chart." A number of exposed pipe features and obstructions were identified with the MBES and SSS data within the H12735 survey area, which corroborates the caution area statement. A large Safety Fairway (FAIRWY) intersected H12735. No controlling depth is reported for the Safety Fairway; survey depths within the charted fairway show good agreement with charted depths varying from 0 to 5 feet. A Fairway Anchorage (ACHARE) intersected the northeastern corner of Survey H12735. No controlling depth is reported for the anchorage area. A charted platform is positioned on the boundary between the Safety Fairway and the Fairway Anchorage at 29-25-36.78 N, 88-55-15.13 W. No new features of significance were identified within the Fairway or Anchorage Area by Survey H12735. Seven (7) bottom samples were acquired to determine bottom characteristics. Bottom samples were assigned in the PRF provided with the Hydrographic Survey Project Instructions. There were no deviations from the assigned bottom sampling plan. A position and description of each sample are provided as attributed SBDARE objects in the FFF. Digital images with identification reference numbers are submitted with the survey data and referenced in the NOAA extended attributes ‘images’ field. No shoreline exists within this survey. Prior survey data exists for this survey area. However, with the exception of the assigned junction surveys, prior data were not investigated. No Aids to navigation (ATONs) exist for this survey. Overhead features do not exist for this survey. An abundance of charted pipelines are located within Survey H12735. Pipes colored magenta represent supply pipelines for oil, gas, chemicals, or water, according to Chart No. 1: Nautical Chart Symbols, Abbreviations and Terms downloaded from the Office of Coast Survey (OCS) website (Figure 24). None of the charted pipelines have a buried depth value (BURDEP). That being said, the majority of the charted pipelines are not visible in the SSS or MBES data. Multiple linear contacts presumed to be exposed sections of charted pipelines were selected in the side scan records. Most were confirmed with MBES coverage. Some sections of pipeline had a measurable height above the seafloor while others had little to no vertical relief. All pipelines visible in the SSS record, were digitized in CARIS SIPS Side Scan Editor as linear pipeline contacts whether buried in a trench or lying exposed on the surface. As mentioned in the DtoN section of this report, 43 exposed pipeline sections were presented within two DtoN submissions for this survey. The exposed pipeline sections and relevant attribution are included in the H12735 FFF. Review of information contained in a shape file (.SHP) downloaded from the Bureau of Ocean Energy Management (BOEM) on October 3, 2014 suggests that there may be several uncharted pipelines within Survey H12735. The BOEM pipeline shape file that intersects with the OPR-J337-KR-15 project area was reprojected to UTM Zone 16N, NAD83 and saved as a .DXF file. The BOEM pipeline DXF file was then visually compared to the charted pipelines within the project area to identify any uncharted BOEM pipelines. Figure 25 provides an overview of the disparity between charted and BOEM-defined pipelines within Survey H12735. The shape file, “ppl_arcs.shp” and re-projected .DXF file, “Pipelines_UTM_16N_NAD83_Meters.dxf” are included with the digital deliverables along with the RNC/ENC charts considered in the chart comparison. BOEM pipeline data were obtained at the following web address: http://www.data.boem.gov/homepg/data_center/mapping/geographic_mapping.asp. On the left, an example of charted pipelines from RNC 11363. On the right, a screen grab from Chart No. 1, Section L Offshore Installations, explains the NOAA chart symbols for the submarine pipelines encountered within OPR-J377-KR-15. H12735_Figure_24_Chart-1_Pipelines.jpg The yellow lines represent BOEM-defined pipelines that are not depicted on RNCs 11353, 11363 and 11361. H12735_Figure_25_Unchd_BOEM_Pipes.jpg No ferry routes or terminals are located within the survey. Sixteen (16) “assigned” platforms were included in the composite Source File (CSF). Twelve (12) of the CSF-assigned platforms were verified visually on the surface and positioned with SSS and/or MBES coverage. New positions are recommended for two (2) of these charted platforms, where the difference between the platform's surveyed position and its charted position was greater than 2mm at the scale of the survey (e.g. 40m for 1:20,000). One of the platforms recommended for a position update was composed of an expansive, multi-towered construction. The extents of the multi-platform feature were not well represented by a single platform point symbol. Therefore, it is recommended that the platform charted at 29-24-01.11 N, 88-58-10.04 W be deleted and replaced with two or more point platform symbols at the new positions of the individual platform towers, as represented in the FFF (Figure 26). Three (3) CSF-assigned platforms were disproved with 100% SSS and Complete Multibeam coverage, and one (1) charted submerged platform was disproved with Complete Multibeam coverage. During a pre-survey chart review, two charted platforms were identifed that were not included in the CSF file. The platforms were investigated by the field team and were verified visually and with MBES coverage at their charted positions of 29-18-58.42 N, 88-55-13.60 W and 29-18-21.65 N, 88-55-18.88 W. The unassigned platforms are included in the FFF. For specific information regarding each verified, updated, or deleted platform see the S-57 final feature file. Existing platform pictures are included under the NOAA Extended Attribute "images." On the left, the surveyed positions of the three-towered platform visible in a SSS mosaic are shown in respect to the charted platform position on RNC 11363, with the recommended new platform positions shown in black. The right image captures the platform's surface presence. H12735_Figure_26_Multi-Tower_Platform.jpg No significant features exist for this survey. OSI does not have knowledge of planned construction or dredging in the H12735 survey area; however, multiple temporary-jack-up rigs were encountered during survey operations, and the depressions left in the seafloor from prior jack-up rig activity are scattered throughout the project area (Figure 27). Multiple jack-up rigs and their depressions left behind in the seafloor were identified in the MBES and SSS data. H12735_Figure_27_Jack-up_Rig.jpg No new surveys or further investigations are recommended for this area. No new insets are recommended for this area. As Chief of Party, field operations for this hydrographic survey were conducted under my direct supervision, with frequent personal checks of progress and adequacy. I have reviewed the attached survey data and reports. All field sheets, this Descriptive Report, and all accompanying records and data are approved. All records are forwarded for final review and processing to the Processing Branch. The survey data meets or exceeds requirements as set forth in the NOS Hydrographic Surveys and Specifications Deliverables Manual, Field Procedures Manual, Letter Instructions, and all HSD Technical Directives. These data are adequate to supersede charted data in their common areas. This survey is complete and no additional work is required with the exception of deficiencies noted in the Descriptive Report. George G. Reynolds Chief of Party 2015-11-19 Data Acquisition and Processing Report 2015-11-19 Horizontal and Vertical Control Report 2015-11-19