OPR-Q328-FA-16North Coast of Unalaska IslandUnalaska IslandNOAA Ship FAIRWEATHERH129382Nateekin Bay to Broad BayAlaskaUnited States50002016CDR Mark Van Waes, NOAANavigable Area2016-07-082016-08-092016-08-22Multibeam Echo SounderMultibeam Echo Sounder BackscattermetersUniversal Transverse Mercator (UTM)UTCPacific Hydrographic BranchThe purpose of this survey is to provide contemporary surveys to update National Ocean Service (NOS) nautical charts. All separates are filed with the hydrographic data. Any revisions to the Descriptive Report (DR) generated during office processing are shown in bold, red italic text. The processing branch maintains the DR as a field unit product, therefore, all information and recommendations within the body of the DR are considered preliminary unless otherwise noted. The final disposition of surveyed features is represented in the OCS nautical chart update products. All pertinent records for this survey, including the DR, are archived at the National Centers for Environmental Information (NCEI) and can be retrieved via http://www.ncei.noaa.gov/.NOAAThe survey area is located in Unalaska, AK, within the sub-locality of Nateekin Bay to Broad Bay.53.9323235278166.64580311153.8685468333166.536984889H12938 sheet limits (in blue) overlaid onto Chart 16530SupportFiles\H12938_Survey_Limits.jpgData for survey H12938 were acquired to the survey limits in accordance with the requirements in the Project Instructions and the National Ocean Service Hydrographic Surveys Specifications and Deliverables (HSSD) dated March 2016, as shown in Figure 1. In all areas where the 4-meter depth contour or the sheet limits were not met, the Navigable Area Limit Line (NALL) was defined by the inshore limit of safe navigation due to the risks of maneuvering the survey vessel in close proximity to the steep and rocky shoreline. An example of this is the foul area north of Hog Island, as shown in Figure 2. One exception is in the southwest corner of Nateekin Bay, where a broad, flat shelf extended into an area deemed not navigationally significant by the hydrographer (see Figure 3). A change to the sheet limits to exclude this area was suggested by the Project Manager, approved by the Alaska Navigation Manager, and granted by the Hydrographic Surveys Division Chief of Operations Branch. A record of this correspondence can be found in Appendix II.H12938 Example of an area not acquired to the 4m depth contour due to kelp/safe navigation near rocksSupportFiles\H12938_Not_meeting_4m.pngH12938 Nateekin Bay deviation from survey limit requirementsSupportFiles\Nateekin_Bay.pngSee attached correspondence regarding modification to the assigned sheet limits.The purpose of this project is to provide contemporary surveys to update National Ocean Service nautical charting products in a high commercial traffic area. This project will cover approximately 9 square nautical miles. This survey is a direct response to the USCG’s request for a hydrographic survey after the July 2015 grounding of a polar ice class vessel, in addition to addressing local pilot requests for modern hydrography to support an increasing amount of vessel traffic in the area.The entire survey is adequate to supersede previous data.Data acquired in H12938 meets multibeam echo sounder (MBES) coverage requirements for complete coverage, as required by the HSSD. This includes crosslines (see Section B.2.1), NOAA allowable uncertainty (see Section B.2.10), and density requirements (see section B.2.11). Additional compliance statistics can be found in the Standards and Compliance Review located in Appendix II of this report.The Standards and Compliance Review is not appended to this report.Inshore limit to 8 meters water depthEither complete coverage or multibeam set line spacing at 25m, as identified in the PRF by CTNARE areas. Refer to HSSD Sections 5.2.2.3, 5.2.2.4, and 5.2.2.1.Greater than 8 meters water depthComplete Coverage. Refer to HSSD Section 5.2.2.3 (Option A).The entirety of H12938 was acquired with complete coverage MBES with backscatter, meeting the requirements listed above and in the HSSD. See Figure 4 for an overview of coverage.H12938 survey coverage (8m combined surface) overlaid onto Chart 16530SupportFiles\H12938_Survey_Coverage.jpgFA 2805097.300000011.040FA 28060131.520000000FA 2807038.2000000000256.940000011.0404.29110009.032016-08-102016-08-112016-08-122016-08-132016-08-142016-08-152016-08-162016-08-172016-08-202016-08-22Refer to the OPR-Q328-FA-16 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.28058.641.1228068.641.1228078.641.12RESON7125MBESApplanixPOS/MV V4Positioning and Attitude SystemRESONSVP71Sound Speed SystemSeaBird19plusConductivity, Temperature, and Depth SensorCrosslines were collected, processed and compared in accordance with section 5.2.4.3 of the HSSD. To evaluate crosslines, an 8-meter CUBE surface using strictly mainscheme lines, and an 8-meter CUBE surface using strictly crosslines were created. From these two surfaces, a difference surface (mainscheme - crosslines = difference surface) was generated at an 8-meter resolution (Figure 5), and is submitted in the Separates II Digital Data folder. Statistics show the mean difference between the depths derived from mainscheme and crosslines was 0.03 meters (with mainscheme being shoaler) with a 95% of nodes falling within 0.63 meters (Figure 6). For the respective depths, the difference surface was compared to the allowable NOAA accuracy standards (Figure 7). In total, 98.76% of the depth differences between H12938 mainscheme and crossline data are within allowable NOAA accuracies (Figure 8). The largest differences exhibited are in areas where the geologic structure of the seafloor is dynamic, such as steep slopes and rocks, as seen in Figure 9.Overview of H12938 crosslinesSupportFiles\Overview of H12938 crosslines.pngH12938 mainscheme and crossline difference statisticsSupportFiles\H12938_crossline_stats.pngDepth differences between H12938 mainscheme and crossline data as compared to NOAA allowable uncertainty standards for the associated depthsSupportFiles\H12938_crossline_allowable_uncertainty.pngCrossline surface statistics showing percentage of nodes meeting NOAA allowable uncertaintySupportFiles\H12938_crossline_noaa_stats.pngAreas where dynamic nature of seafloor affects the NOAA allowable uncertaintySupportFiles\Example_crossline_NOAAness.png00.06Discrete Zoning00.04ERS via PMVD28052N/A0.528062N/A0.528072N/A0.5In addition to the usual a priori estimates of uncertainty provided via device models for vessel motion, discrete zoning tides and PMVD, real-time and post-processed uncertainty sources were also incorporated into the depth estimates of survey H12938. Real-time uncertainties were provided via Reson 7125 MBES data and Applanix Delayed Heave RMS. Following post-processing of vessel motion, real time uncertainties of vessel roll, pitch, gyro and navigation were applied in CARIS HIPS and SIPS via a Smoothed Best Estimate of Trajectory (SBET) RMS file generated in Applanix POSPac. H12938 junctions with two adjacent surveys from this project (H12937, H12939), and two surveys from prior projects (F00601, F00663), as shown in Figure 10. Data overlap between all surveys was achieved. These areas of overlap were reviewed with CARIS HIPS and SIPS by surface differencing (at equal resolutions) to assess surface agreement. The multibeam data were also examined in CARIS Subset Editor for consistency and agreement. The junctions with H12938 generally exceed the NOAA allowable uncertainty in their areas of overlap. For all junctions with H12938, a negative difference indicates H12938 was shoaler, and a positive difference indicates H12938 was deeper.Junction between H12938 and H12937, H12939, F00601, and F00663SupportFiles\H12938_Junction_Overview.pngH1293750002016NOAA Ship FAIRWEATHERSESurface differencing in CARIS HIPS and SIPS was used to assess junction agreement between the 8 meter combined surface from H12938 and the 8 meter combined surface from H12937. H12938 and H12937 junction in two distinct areas. The northern junction is depicted in Figure 11, and the southern junction is depicted in Figure 12. The statistical analysis of the difference surface shows a mean of 0.00 meters with 95% of all nodes having a maximum deviation of +/- 0.83 meters, as seen in Figure 13. The largest differences are seen in rocky areas and areas with steep slopes. In addition, a comparison surface was created between the difference surface and the NOAA allowable uncertainty (Figures 14 and 15). It was found that 96.37% of nodes are within the allowable NOAA uncertainty (Figure 16).Northern difference surface between H12938 and junctioning survey H12937SupportFiles\H12938_H12937_junction_North1.pngSouthern difference surface between H12938 and junctioning survey H12937SupportFiles\H12938_H12937_junction.pngDifference surface statistics between H12938 and H12937 (8 meter combined surface)SupportFiles\H12938_H12937_junction_stats.pngNorthern difference surface compliance with regard to NOAA allowable uncertainty between H12938 and H12937SupportFiles\H12938_H12937_NOAAness_North.pngSouthern difference surface compliance with regard to NOAA allowable uncertainty between H12938 and H12937SupportFiles\H12938_H12937_NOAAness.pngDifference surface statistics between H12938 and H12937 showing percentage of nodes meeting NOAA allowable uncertaintySupportFiles\H12938_H12937_NOAA_Stats.pngH12939200002016NOAA Ship FAIRWEATHERNSurface differencing in CARIS HIPS and SIPS was used to assess junction agreement between the 8 meter surface from H12938 and the 8 meter surface from H12939. A detailed graphical overview can be seen in Figure 17. The statistical analysis of the difference surface shows a mean of 0.02 meters with 95% of all nodes having a maximum deviation of +/- 0.77 meters, as seen in Figure 18. In addition, a comparison surface was created between the difference surface and the NOAA allowable uncertainty (Figure 19). It was found that 98.90% of nodes are within the allowable NOAA uncertainty (Figure 20).Difference surface between H12938 and junctioning survey H12939 SupportFiles\H12938_H12939_8m_junction.pngDifference surface statistics between H12938 and H12937 (8 meter surface)SupportFiles\H12938_H12939_8m.pngDifference surface compliance with regard to NOAA allowable uncertainty between H12938 and H12939SupportFiles\H12938_H12939_8m_NOAA.pngDifference surface statistics between H12938 and H12939 showing percentage of nodes meeting NOAA allowable uncertaintySupportFiles\H12938_H12939_8m_NOAA_stats.pngF0060150002011NOAA Ship FAIRWEATHERWSurface differencing in CARIS HIPS and SIPS was used to assess junction agreement between the 8 meter combined surface from H12938 and the 8 meter combined surface from F00601. A detailed graphical overview can be seen in Figure 21. The statistical analysis of the difference surface shows a mean of 0.05 meters with 95% of all nodes having a maximum deviation of +/- 0.45 meters, as seen in Figure 22. The largest differences were observed in rocky areas. In addition, a comparison surface was created between the difference surface and the NOAA allowable uncertainty (Figure 23). It was found that 99.38% of nodes are within the allowable NOAA uncertainty (Figure 24).Difference surface between H12938 and junctioning survey F00601SupportFiles\H12938_F00601_Difference.pngDifference surface statistics between H12938 and F00601 (8 meter combined surface)SupportFiles\H12938_F00601_8m_Difference.pngDifference surface compliance with regard to NOAA allowable uncertainty between H12938 and F00601SupportFiles\H12938_F00601_NOAAness.pngDifference surface statistics between H12938 and F00601 showing percentage of nodes meeting NOAA allowable uncertaintySupportFiles\H12938_F00601_NOAA_stats.pngF00663100002015NOAA Ship FAIRWEATHERESurface differencing in CARIS HIPS and SIPS was used to assess junction agreement between the 1 meter surface from H12938 and the 1 meter surface from F00663. A detailed graphical overview can be seen in Figure 25. The statistical analysis of the difference surface shows a mean of 0.06 meters with 95% of all nodes having a maximum deviation of +/- 0.28 meters, as seen in Figure 26. In addition, a comparison surface was created between the difference surface and the NOAA allowable uncertainty (Figure 27). It was found that 99.99% of nodes are within the allowable NOAA uncertainty (Figure 28).Difference surface between H12938 and junctioning survey F00663SupportFiles\H12938_F00663_Difference.pngDifference surface statistics between H12938 and F00663 (1 meter surface)SupportFiles\H12938_F00663_junction_stats.pngDifference surface compliance with regard to NOAA allowable uncertainty between H12938 and F00663SupportFiles\H12938_F00663_NOAAness.pngDifference surface statistics between H12938 and F00663 showing percentage of nodes meeting NOAA allowable uncertaintySupportFiles\H12938_F00663_NOAA_stats.pngSonar system quality control checks were conducted as detailed in the quality control section of the DAPR.None ExistThere were no conditions or deficiencies that affected equipment operational effectiveness.Sea Grass and KelpKelp and sea grass were present throughout the survey area and at times indistinguishable from the seafloor (Figure 29). In areas where they were distinguishable, the soundings on the vegetation were rejected to enable more accurate representation of the true seafloor. Where vegetation was indistinguishable, all soundings were retained. Furthermore, in some areas patches of dense kelp prohibited safe navigation of the survey vessels. The limits of these areas were then used to define the NALL (Figure 30).Example of kelp in the data (5x vertical exaggeration) SupportFiles\Kelp_Example.pngSheet limit not met due to kelp and debrisSupportFiles\H!2938_4m_example.pngSound SpeedThroughout the survey area of H12938 there are instances of vertical offsets that appear to be due to changes in sound speed. These issues were observed primarily in the deeper water west of Hog Island (see Figure 31), and result in the outer beams of tracklines generally bending downwards, or "frowning". This offset persists across multiple sound velocity casts, suggesting that the issue may have been due to a surface sound velocity anomaly. All sound velocity casts were conducted as referenced below in Section B.2.7. In general, soundings are within the HSSD specifications for sound speed uncertainty for their respective depths, and had a negligible impact on the Finalized CUBE surface. See Figure 32 for a graphical representation of sound speed influence. H12938 Area of vertical offsets due to sound speed influenceSupportFiles\H12938_sound_speed.pngH12938 Subset of data "frowning" due to sound speed issues (gray soundings were rejected)SupportFiles\H12938_sound_speed_subset.pngCasts were conducted at a minimum of at least one per every 4 hours during launch acquisition. Casts were conducted more often in areas where the input of freshwater had an effect on the speed of sound in the water column and when there was a change in surface sound velocity greater than two meters per second.All equipment and survey methods were used as detailed in the DAPR.HolidaysH12938 data were reviewed in CARIS HIPS and SIPS for holidays in accordance with section 5.2.2.3 of the HSSD. All finalized surfaces were scanned for holidays via Pydro QC Tools Holiday Finder tool in conjunction with a visual inspection by the hydrographer. Although numerous apparent holidays were identified in the finalized surfaces by Holiday Finder, all were examined and determined to be from areas where adjoining finalized surfaces covered the gap (e.g. a holiday in the 2 meter finalized surface was covered by the 1 meter finalized surface due to the area being shoaler than the depth range for the 2 meter surface) as shown in Figure 33. Area where adjoining finalized 1 meter surface (in blue) covers flagged holiday in the 2 meter finalized surface (in red)SupportFiles\H12938_false_holiday.pngNOAA Allowable UncertaintyTo verify that all data meets the accuracy specifications as stated in HSSD Section 5.1.3, a child layer titled "NOAA_Allowable_1" was created for each of the 1-meter, 2-meter, 4-meter, and 8-meter (72-100m) finalized surfaces, and a child layer titled "NOAA_Allowable_2" for the 8-meter (100-170.74m) finalized surface using the equations stated in Section C.2.1 of the DAPR. These surfaces were then analyzed using the Pydro QC Tools Grid QA feature to determine what percentage of each surface meets specifications. Figure 34 shows an overview of the NOAA Allowable Uncertainty layers for all surfaces. Figure 35 shows the corresponding statistics for each individual surface. Overall, 99.95% of nodes within all surfaces meet or exceed NOAA Allowable Uncertainty specifications for H12938. For individual graphs per surface of density requirements, see the Standards and Compliance Review located in Appendix II.H12938 overview of NOAA allowable uncertaintySupportFiles\NOAA_Allowable_Uncertainty_overview.jpgH12938 NOAA uncertainty statisticsSupportFiles\NOAA_Allowable_Uncertainty_Statistics.pngThe Standards and Compliance Review is not appended to this report.DensityFinalized surfaces were analyzed using the Pydro QC Tools Grid QA feature and an overview of the results is shown in Figure 36 below. Density requirements for H12938 were achieved with at least 99.93% of finalized surface nodes containing five or more soundings as required by HSSD Section 5.2.2.3. Statistics of the density compliance are shown in Figure 37. For individual graphs (per surface) of density requirements, see the Standards and Compliance Review located in Appendix II.H12938 Density overviewSupportFiles\H12938_Density_Overview.pngH12938 Density overviewSupportFiles\H12938_Density_Statistics.pngThe Standards and Compliance Review is not appended to this report.All data reduction procedures conform to those detailed in the DAPR.All sounding systems were calibrated as detailed in the DAPR.Raw backscatter data were logged as .7k files and have been processed by the field unit to review data quality as well as to modify bottom sample locations. The corresponding mosaics, tiffs, projects and GSF files have been submitted with this project. Figure 38 shows an overview of the mosaic created from H12938 survey data.H12938 Backscatter mosaicSupportFiles\H12938_Backscatter_Mosaic.pngTeledyne CARISHIPS and SIPS9.1QPSFledermaus FMGT7.5.3NOAA Extended Attribute Files version 5.4H12938_MB_1m_MLLWCUBE1NOAA_1mComplete MBESH12938_MB_2m_MLLWCUBE2NOAA_2mComplete MBESH12938_MB_4m_MLLWCUBE4NOAA_4mComplete MBESH12938_MB_8m_MLLWCUBE8NOAA_8mComplete MBESH12938_MB_1m_MLLW_FinalCUBE1020NOAA_1mComplete MBESH12938_MB_2m_MLLW_FinalCUBE21840NOAA_2mComplete MBESH12938_MB_4m_MLLW_FinalCUBE43680NOAA_4mComplete MBESH12938_MB_8m_MLLW_FinalCUBE872170.74NOAA_8mComplete MBESThe NOAA CUBE parameters defined in the HSSD were used for the creation of all CUBE surfaces in survey H12938, with the exception of the 8 meter surface. As a minimal percentage by area of H12938 met the depth threshold for the 16 meter depth range, a waiver to extend the 8 meter surface depth and not submit a 16 meter surface was granted from the Hydrographic Survey Division Operations Branch, and is located in Appendix II. All data within the extended 8 meter surface still meets coverage requirements as defined by the HSSD. The surfaces have been reviewed where noisy data, or "fliers", are incorporated into the gridded solutions causing the surface to be shoaler or deeper than the true sea floor. Where these spurious soundings cause the gridded surface to vary from the reliably measured seabed by greater than the maximum allowable Total Vertical Uncertainty at that depth, noisy data were rejected by the Hydrographer and the surface recomputed. Flier Finder v3, part of the QC Tools package within Pydro, was used to assist the search for spurious soundings following gross cleaning. Flier Finder was run multiple times for each surface, reducing the flier height value for each consecutive run. This allowed Flier Finder to accurately and quickly identify gross fliers, but as the flier height was reduced the effectiveness of the tool diminished. With smaller heights Flier Finder began to incorrectly flag dynamic aspects of the seafloor such as steep drop offs and rocky areas as fliers, resulting in hundreds of false positives. At this point, the hydrographer ceased using the tool and returned to manual cleaning for these dynamic regions of seafloor.The NOAA Cube Parameters were used for the creation of all surfaces delivered as part of H12938, including the 8 meter surface. See attached waiver regarding the extension of the depth threshold for the 8 meter surface out to 170.74 meters, the maximum depth of the survey.Data LogsData acquisition and processing notes are included in the acquisition and processing logs, and additional processing such as final tide and sound velocity application are noted in the H12938 Data Log spreadsheet. All data logs are submitted digitally in the Separates I folder.Designated SoundingsH12938 contains one designated sounding in accordance with HSSD Section 5.2.1.2.3. The designated sounding signifies a new rock along the western side of the entrance to Nateekin Bay (see Figure 39).H12938 Designated soundingSupportFiles\H12938_Designated_soundings.pngNo control stations were installed by the field party, and as such, no Horizontal and Vertical Control Report (HVCR) is submitted with this report. All relevant discussion regarding horizontal and vertical control may be found in the discussion below.Mean Lower Low WaterUnalaska, AK9462620Discrete Zoning9462620.tidFinal ApprovedQ328FA2016CORP.zdfFinal2016-08-262016-09-08Initial reduction of acquired data to MLLW was accomplished via traditional tidal means using the discrete zoning provided by HSD-OPS. Following the successful application of SBETs and computation of an Ellipsoidally Referenced Zone Tide (ERZT) separation model, ERS methods were used for reducing data to MLLW. Preliminary zoning was accepted as the final zoning for project OPR-Q328-FA-16.See attached Tide Note dated September 7, 2016.ERS via Poor Mans VDATUMQ328FA2016CORP_PMVDERZT_UTM-WGS84-8N_WGS84-MLLW_100m.csarERS methods were used as the final means of reducing H12938 to MLLW for submission. Data were initially reduced via traditional tidal means until an Ellipsoidally Referenced Zone Tide (ERZT) separation model could be calculated. This empirically derived model was then checked for consistency and compared to the Poor Man's VDatum (PMVD) separation model provided with the Project Instructions. The PMVD separation model was then vertically shifted such that the average difference between these two separation models is zero. The vertical shift de-biases the PMVD separation model, correcting for local variations that cannot be effectively modeled by the PMVD. In areas where the PMVD model did not have sufficient coverage, such as nearshore areas, the ERZT surface was checked for consistency and appended to the model. For further information, see the ERS Capability Memo, submitted under a separate cover. See attached ERS Capability Memorandum dated November 7, 2016.World Geodetic System of 1984 (WGS84)UTM Zone 3 NorthSingle BaseAV09Haystack_AK2004Vessel kinematic data were post-processed using Applanix POSPac processing software with SingleBase positioning methods as described in the DAPR. Smooth Best Estimate of Trajectory (SBET) and associated error (RMS) data were applied to all MBES data in CARIS HIPS. For further details regarding the processing and quality control checks performed see the H12938 POSPAC Processing Logs spreadsheet located in the Separates folder. See also the OPR-Q328-FA-16 Horizontal and Vertical Control Report, submitted under separate cover. Hydrographic Technical Directive (HTD) 2016-3, which revises the horizontal datum requirement was released after the Project Instructions were issued for OPR-Q328-FA-16. A waiver to maintain WGS84 as the datum for submission was granted by the Hydrographic Survey Division Operations Branch. This correspondence has been included in Appendix II. See attached correspondence regarding the waiver to acquire and process the survey in WGS84.WAASDuring real-time acquisition, launches 2805, 2806 and 2807 received correctors from the Wide Area Augmentation System (WAAS) for increased accuracies similar to USCG DGPS stations. WAAS and SBETs were the sole methods of positioning for survey H12938. No DGPS stations were available for realtime horizontal control.Comparisons were performed between survey H12938 and Charts 16530 and 16528 as well as ENCs US5AK6EM and US5AK6CM using CARIS HIPS and SIPS sounding and contour layers derived from the 8 meter combined surface. The contours and soundings were overlaid on the chart to assess differences between the surveyed and charted depths. ENCs were compared to an 8 meter combined grid by extracting all soundings from the chart and creating an interpolated TIN surface which could be differenced with the combined surface from H12938. All data from H12938 should supersede charted data. In general, surveyed sounding agree with the majority of the charted depths. A full discussion of the disagreements follows below.1653025241000072010-052016-09-132016-10-10The charted soundings and contours of Chart 16530 are identical to those found on ENC US5AK6EM. As such, all discussions regarding comparisons between surveyed soundings and charted depths are covered under the ENC US5AK6EM discussion below. 16528252240000182012-092016-09-102016-09-10The charted soundings and contours of Chart 16528 are identical to those found on ENC US5AK6CM. As such, all discussions regarding comparisons between surveyed soundings and charted depths are covered under the ENC US5AK6CM discussion below. US5AK6EM1000092016-03-172016-03-17falseSoundings from H12938 are in a general agreement with charted depths on ENC US5AK6EM, with most depths agreeing to 1-2 fathoms. The largest differences are seen in rocky areas as well as areas with steep slopes, where differences are observed up to 7 fathoms, as seen in Figure 42. To more accurately visualize trends within these differences, an 8 meter TIN surface was interpolated from the ENC sounding layer. This surface was then differenced with a corresponding 8 meter surface from H12938. Figure 40 shows an overview of the difference surfaces generated between the 8 meter combined surfaces from H12938 and the 8 meter TIN surfaces generated from ENC Charts US5AK6CM and US5AK6EM. In this difference surface red colors indicate H12938 was shoaler than the ENCs, green colors indicate agreement, and blue colors indicate H12938 was deeper than the ENCs. The mean difference between surveyed soundings from H12938 and the charted depths on ENC US5AK6EM is 0.37 meters, with 95% of nodes having a deviation of +/- 7.44 meters as shown in Figure 41. Contours from H12938 are in general agreement with the charted contours on ENC US5AK6EM as shown in Figure 42. An area where the survey derived contours deviate significantly from the charted contours is illustrated in Figure 44.Difference surface between H12938 and interpolated TIN surface from Charts US5AK6CM (north) and US5AK6EM (south)SupportFiles\H12938_ENC_Comparison_combined.pngDifference surface statistics between H12938 and interpolated TIN surface from US5AK6EMSupportFiles\H12938_ENC_comparison_Stats.pngClose up of area west of Hog Island where significant differences exist between H12938 soundings (in red) and ENC US5AK6EM depths (in black)SupportFiles\sounding_discrepency_w_Hog.pngOverview of H12938 contours overlaid onto US5AK6EM and US5AK6CMSupportFiles\H12938_Contour_Overview.pngArea west of Amaknak Island where significant differences exist between H12938 contours and US5AK6EM contoursSupportFiles\H12938_Contour_Discrepency.pngUS5AK6CM40000132015-11-252015-11-25falseSoundings from H12938 are in a general agreement with charted depths on ENC US5AK6CM, with most depths agreeing to 1-2 fathoms. To more accurately visualize trends within these differences, an 8 meter TIN surface was interpolated from the ENC sounding layer. This surface was then differenced with a corresponding 8 meter surface from H12938 and visualized in Figure 40 above. In this difference surface red colors indicate H12938 was shoaler than ENC US5AK6CM, green colors indicate agreement, and blue colors indicate H12938 was deeper than ENC US5AK6CM. The mean difference between surveyed soundings from H12938 and the charted depths on ENC US5AK6CM is 0.46 meters, with 95% of nodes having a deviation of +/- 12.02 meters as shown in Figure 45. Contours from H12938 are in general agreement with the charted contours on ENC US5AK6CM as shown in Figure 43 above. The hydrographer recommends adding a 5 fathom contour to US5AK6CM to provide continuity with US5AK6EM to the mariner, as shown in Figure 46.Difference surface statistics between H12938 and interpolated TIN surface from US5AK6CMSupportFiles\H12938_8m_ENC_Comparison_North.pngProposed addition of 5fm contour to US5AK6CM in Broad BaySupportFiles\H12938_contour_proposed_addition.pngNo Maritime Boundary Points were assigned for this survey.All assigned features within the NALL were addressed and are included in the H12938 Final Feature File. Assigned features inshore of the NALL were given the description "Not Addressed" with remarks "Retain as charted, not investigated due to being inshore of NALL" in accordance with HSSD 7.3.1.Chart 16530 has 'Unexploded ordnance (reported 2013)' annotated at three locations in Unalaska Bay. Although the bathymetry acquired as part of H12938 does not indicate potentially hazardous features in the vicinity of the charted notes, it is recommended that all notes be retained as a precaution to mariners who anchor in the area. Survey H12938 contains 12 new features that are addressed in the H12938_Final_Feature_File. Of these features, 11 are new Seabed Areas and 1 is a new Underwater Rock. No Danger to Navigation Reports were submitted for this survey.Two potentially hazardous features were discovered within the H12938 survey area. An uncharted rock approximately 70 meters from the charted foul area at the western mouth of Nateekin Bay with a least depth of 3.52 meters was found during MBES acquisition (See Figure 47). This rock has been added to the H12938_Final_Feature_File as noted above in Section D.1.5. A second potentially hazardous feature is a large underwater rock or ledge with a least depth of 1.65 meters, found on the eastern side of Nateekin Bay along the NALL (See Figure 48). While this feature does pull the surface in two discrete locations, it is not accurately represented by the CUBE surface (See Figure 49). Both of these features, although significant, were found in areas not exposed to vessel traffic. H12938 Uncharted rock near Nateekin BaySupportFiles\H12938_Uncharted_Rock.pngH12938 Location of uncharted rock on western side of Nateekin BaySupportFiles\H12938_ledge.pngH12938 Subset of uncharted rock showing inaccurate representation of CUBE surfaceSupportFiles\H12938_ledge_subset.pngAs shown in Figure 49, a least depth could not be unequivocally obtained on the second potentially hazardous feature because the feature was only partially ensonified. The depth of the offshore edge of the feature, insofar as the partial coverage obtained, is valid and adequately represented by the CUBE surface. It was recommended during office compilation that the adjacent foul area be extended to encompass the feature.No channels exist for this survey. There are no designated anchorages, precautionary areas, safety fairways, traffic separation schemes, pilot boarding areas, or channel and range lines within the survey limits.Eleven bottom samples were acquired in accordance with the Project Instructions for survey H12938. Nine bottom samples were acquired as assigned, and two were moved based on the backscatter data to investigate the differing returns in the northeast corner of H12938. All bottom samples were entered in the H12938 Final Feature File. See Figure 50 for a graphical overview of sample locations.H12938 bottom sample locationsSupportFiles\H12938_Bottom_Samples.pngH12938 survey limits extended to the NALL (see Section A.1) and all features within these limits were addressed in the H12938 Final Feature File. All features inshore of the NALL were addressed in the Final Feature File with the description of "Not Addressed" and remarks of "Retain as charted, not investigated due to being inshore of NALL" as per HSSD Section 7.3.1. Annotations, information, and diagrams collected on DP forms during field operations are scanned and included in the Separates I Detached Positions folder. No prior survey comparisons exist for this survey.All ATONs located within H12938 were on station and serving their intended purpose.No overhead features exist for this survey.Although significant abandoned submarine cable areas are charted throughout H12938, no cables were observed in the bathymetry data. No ferry routes or terminals exist for this survey.No platforms exist for this survey.No Significant Features exist for this survey.No present or planned construction or dredging exist within the survey limits.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.CDR Mark Van Waes, NOAAChief of Party 2016-11-19LT Bart Buesseler, NOAAField Operations Officer2016-11-19HCST Douglas BravoChief Survey Technician2016-11-19HST Sam CandioSheet Manager2016-11-19Data Acquisition and Processing Report2016-10-19Coast Pilot Report2016-10-26