OPR-R300-KR-16Etolin StraitBering SeaTerraSond LimitedH128714Registry Instructions13 NM North of Cape EtolinAlaskaUnited States400002016Andrew OrthmannNavigable Area2016-05-122016-06-262016-08-02Multibeam Echo SounderSide Scan SonarmetersWGS84UTCPacific Hydrographic BranchContractorA navigable area survey (H12871) was conducted in the area 13 NM North of Cape Etolin, Alaska, in accordance with the NOAA, National Ocean Service, Statement of Work (SOW), OPR-R300-KR-16, dated February 19th, 2016 (modifications dated July 15th, 2016) and Hydrographic Survey Project Instructions dated May 12th, 2016 (modifications dated July 20th, 2016). Hydrographic survey data was acquired from June 26th through August 1st, 2016. Tidal data was collected from mid-June through late September, 2016. An additional contract modification, "Mod2", issued February 17th, 2017, extended the deliverables submission deadline to March 13th, 2017, due to delays associated with issuance of the final TCARI tide grid. The survey area is centered on the north approach to Etolin Strait, a navigable passage off of the southwest Alaska coast. Nunivak Island lies to the southwest, with Nelson Island and mainland Alaska to the east. This relatively remote region of the Arctic is covered, or heavily influenced, by sea ice for a large portion of the year, presenting a limited ice-free season with open navigable water from approximately June through October. Vessel traffic in the region primarily consists of barges serving nearby communities or transiting through the area to other points along Alaska's west and north coasts, bringing fuel and supplies, as well as some freighter traffic. Nunivak Island provides some of the only protection available for vessels transiting Alaska's southwest coast, a region that frequently experiences inclement weather and poor sea conditions. Traffic is relatively sparse, but has been increasing in recent years along with economic and scientific interest in the Arctic. Nearby communities are small and primarily subsistence-based. Mekoryuk (2010 population 191), located south of the survey area on Nunivak Island, is the largest nearby community. The region is not connected to the road system and communities depend on air services for connections to Bethel and on to Anchorage. No facilities exist nearby for supporting or servicing larger vessels, with Bethel (approximately 250 NM transit) and Nome (approximately 200 NM transit) the closest port options for fueling, or limited services. During this survey--which utilized a 105' research vessel--Bethel was used for resupply, largely due to a more protected transit route. However, larger or deeper drafted vessels may favor Nome. TerraSond conducted multibeam echosounder (MBES) and side scan sonar (SSS) operations in the area in accordance with the project instructions, which specified areas requiring complete coverage (100% SSS with concurrent complete coverage MBES) and areas requiring set-spaced MBES-only. Other requirements included tidal data collection and bottom sampling. 60.894427166.78148260.39692165.537457Survey extents and overview.SupportFiles\1_H12871_SurveyExtents.jpgSurvey limits were acquired in accordance with the requirements in the Project Instructions and the HSSD, with exceptions noted below. 1. Survey extents were modified on the SE side from the extents provided in the Project Reference File (PRF) with the Project Instructions. The assigned sheet boundary in H12871 at approximately 60-27-20 N, 165-41-53 W was shifted to the SE by about 6 km (into the planned area for junctioning survey H12869). This was done to optimize line planning prior to commencement of survey operations, so that survey lines would better follow natural seafloor contours. Note that this resulted in increased area falling within this survey and decreased area falling within H12869. The affected area received coverage to identical specifications regardless. The inshore limit of hydrography, being the farthest offshore of either the 4 m depth contour, or a line defined by the distance seaward from the MHW line, which is equivalent to 0.8 mm at the scale of the largest scale nautical chart, was not encountered on this survey.The purpose of this project is to provide contemporary surveys to update National Ocean Service (NOS) nautical charting products. The project (of which this survey sheet is one of eight separate, adjacent sheets) covered approximately 570 SNM of seafloor, all Priority 2 area as identified in the 2012 NOAA Hydrographic Survey Priorities document. There is an emerging need to provide modern hydrography in the Arctic to update nautical chart products. In this project area, north of Nunivak Island, deep-draft traffic is operating in relative shoals that have not been surveyed in over 100 years. A 600' chemical tanker (Champion Ebony) grounded on an uncharted shoal at the south approaches to Etolin Strait on June 24th, 2016, just days before survey operations were scheduled to commence. Fortunately, no discharge occurred, but the incident emphasized the need for chart updates in the area. Survey data from this project is intended to supersede all prior survey data in the common area and support larger scale nautical chart products.The entire survey is adequate to supersede previous data.All waters in defined survey corridorFull coverage: 100% Side Scan Sonar with concurrent Multibeam and BackscatterAll survey areas outside of defined survey corridorSet-spaced MBES: 500 m set line spacing Multibeam and BackscatterCoverage requirements were met, with any exceptions noted below. As a relatively large survey area, the sheet was broken down into four roughly equivalent sized survey blocks. These were named "D1" in the north, ending with "D4" in the south. Coverage requirements were met differently by block, though all received complete coverage. D1: The area received 200% SSS in general. D2: The area received 200% SSS in general. D3: The area received 100% SSS coverage. Some small along-track gaps in the coverage are an artifact of SSS processing due to abrupt layback adjustments in processing -- the areas received coverage nonetheless. D4: The area received 200% SSS in general. Note that SSS alongtrack gaps in 100% coverages were covered by the 2nd 100% pass. 200% SSS was not required but was incidentally acquired for the majority of the area. Deeper portions of the survey area also received complete MBES coverage. No areas within this survey were assigned for set-spaced MBES. Splits: Splits were not acquired. Charted depths shoaler than survey depths did not fall between two survey lines given the scale of the affected chart. Shoals, contours, and significant deeps were adequately defined by the mainscheme lines.Survey overview showing coverage.SupportFiles\2_H12871_Coverage.jpgQualifier 105000005180900ASV-CW50000050601700000010240108010.510000482016-06-262016-06-272016-06-282016-06-302016-07-012016-07-022016-07-132016-07-142016-07-312016-08-01Last day of acquisition for bottom samples was 8/2/2016. Actual crosslines for Qualifier 105 is 72 linear nautical miles.Refer to the 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.Qualifier 105321.8ASV-CW55.50.5The Qualifier 105 (Q105) is a 32 m aluminum hull vessel owned and operated by Support Vessels of Alaska. The Q105 acquired all multibeam data and provided housing and facilities for on-site data processing. The vessel also collected bottom samples, deployed BMPG tide gauges, and deployed/recovered the ASV-CW5 vessel. The ASV-CW5 (C-Worker 5) is a 5.5 m aluminum hull Autonomous Surface Vessel (ASV) owned and operated by ASV Global. The ASV was operated in an unmanned, but monitored mode, collecting SSS and MBES data in close proximity to the Q105. Refer to the DAPR for vessel photos, offset diagrams, and more information on vessel operations.Teledyne ResonSeabat 7101MBESApplanixPOSMV 320 V5Positioning and AttitudeApplanixPOSMV 320 V4Positioning and AttitudeValeportRapid SVT 200BarSound Speed ProfilerTeledyne OceanscienceRapidCASTSound Speed Profiler Deployment SystemTrimble5700Base StationSea-Bird ElectronicsSBE 26+Submerged Tide GaugeDAA (YSI - Xylem)WaterLOG H-350XLVented Tide GaugeAML OceanographicMinosX with Xchange SensorsConductivity and Temperature GaugesEdgeTech4200-MPSSSDetails on equipment specifications, configurations, quality control methodology, and methods of operation are described in the DAPR.Crosslines were acquired in accordance with the requirements described in Section 5.2.4.3 of the 2016 HSSD. Effort was made to ensure crosslines had good temporal and geographic distribution, were run so as to enable maximal nadir-to-nadir comparisons, and percent of mainscheme LNM requirements were achieved (4% for complete coverage areas, and 8% for set-spacing coverage areas). Since the complete coverage areas utilized SSS, and therefore, had minimal MBES swath overlap in many locations, the higher standard of 8% was assumed (and achieved) sheet-wide. Crosslines were conducted with both vessels to ensure there was ample overlap for inter-vessel comparisons, with each vessel crossing the other's mainscheme lines. Since the two vessels worked in close proximity and ran parallel lines, crosslines were often collected in sets, with one vessel on each adjacent line. The crossline analysis was conducted using CARIS HIPS “QC Report” routine. Every crossline was selected and run through the process, which calculated the depth difference between each accepted crossline sounding and a QC BASE (CUBE-type, 2 m resolution) surface’s depth layer created from the mainscheme data. QC BASE surfaces were created with the same parameters used for 2 m surfaces as the final surfaces, with the important distinction that the QC BASE surfaces did not include crosslines so as to not bias the QC report results. Differences in depth were grouped by beam number and statistics computed, which included the percentage of soundings with differences from the BASE surface falling within IHO Order 1. When at least 95% of the sounding differences exceed IHO Order 1, the crossline was considered to “pass,” but when less than 95% of the soundings compare within IHO Order 1, the crossline was considered to “fail.” A 5% (or less) failure rate was considered acceptable since this approach compares soundings to a surface, instead of a surface to a surface. Results: Agreement between the BASE surfaces and crossline soundings is excellent. The vast majority of crossline comparisons pass with 95% (or more) of soundings comparing to within IHO Order 1. Failures were investigated and revealed that the primary cause was vertical busts due to tidal error. 5 out of 57 crosslines, (0061-ASV-183-D4XL12, 0062-ASV-183-D4XL06, 0034-Q105-183-D3XL05, 0486-Q105-214-D3XL05, 0487-Q105-214-D3XL06) were found to have some failing beams, usually in the outer part of the swath. Despite the failure of these crossline soundings, final surfaces are within specifications. Refer to Separate II: Digital Data for the detailed Crossline QC Reports.Actual crossline percentage total was 9.6%.0.0380.148TCARIQualifier 10501.0350.025ASV-CW501.0350.025All soundings were assigned a horizontal and vertical value for estimated total propagated uncertainty (TPU). Refer to the DAPR for more detail concerning the parameters and methods used for computation of sounding uncertainty. Note that fixed tide error values (0.038 m measured, 0.148 m zoning) entered during TPU computation were project-wide error averages for tide zones that were ignored by CARIS during TPU computation in favor of real-time tide error estimates loaded coincident with the TCARI model. Therefore, these static error estimates for tide zoning error did not affect final TPU computations. Real-time error estimates for attitude, positioning, and tide were used over fixed error estimates defined in the HVF. Exceptions, if they exist, are listed in Section B.3 of this report. The BASE surfaces were finalized in CARIS HIPS, so that the final uncertainty value for each grid cell is the greater of either standard deviation, or uncertainty. The uncertainty layer of each final surface was then examined for areas of uncertainty that exceeded IHO Order 1. Uncertainty for the surfaces ranged from 0.25 to 0.83 m for the 1 m surface and 0.24 to 0.71 m for the 2 m surface. The vast majority of grid cells have uncertainty values within IHO Order 1. Few exceeded IHO Order 1. Highest uncertainties were found in areas of varying bottom topography such as slopes and near bottom features where high standard deviations are caused by the wide depth ranges of soundings contributing to each grid cell, outer edges of multibeam swathes without adjacent line overlap, and areas exhibiting sound speed, motion artifact error, or tidal error. Despite elevated TPU values for these grid cells, the surface data is within specifications. This survey junctions with two contemporary surveys: H12869 and H12870. These surveys were conducted concurrently with this survey as part of the overall project, OPR-R300-KR-16. Difference surface methodology was used for the junction comparison. The depth layer from 2 m resolution CUBE surfaces from each survey were differenced from each other in CARIS HIPS, resulting in a difference surface. Values were extracted and statistics generated to quantify agreement. Any areas of significant disagreement, generally those exceeding IHO Order 1, were investigated to determine the cause. Survey junctions with this sheet.SupportFiles\6_H12871_Junctions.jpgH12869400002016TerraSondSEAgreement is excellent, averaging 0.012 m, with a standard deviation of 0.194 m, with differences falling in a range of -0.774 to 0.752 m. Few exceed IHO Order 1. Those exceeding IHO Order 1 were examined and determined to be primarily due to tidal bust. Despite the minor disagreement of these grid cells, final surfaces are within specification.H12870400002016TerraSondSAgreement is excellent, averaging 0.082 m, with a standard deviation of 0.164 m, with differences falling in a range of -0.591 to 0.571 m. All agree within IHO Order 1.Echosounder confidence checks consisting of bar checks, lead lines, and inter-vessel acoustic comparisons were undertaken on this project. Results were good, with agreement averaging 0.009 m for bar checks, 0.190 m for lead lines, and 0.059 m for inter-vessel acoustic comparisons . Refer to the bar check, lead line, and echosounder depth comparison logs available in Separate I: Acquisition and Processing Logs for specific results. Refer to the project DAPR for more information regarding QC checks methodology.7101 Beam PatternA distinct beam pattern was obvious in the data set in certain areas, with a fuzziness or “horn” like features on both sides of nadir on multibeam swaths, coinciding with the bottom detection shift from phase to amplitude detection. The pattern is common with Reson 8101/7101 multibeam echosounders in certain bottom types. Power and range settings were adjusted in acquisition to minimize the issue, with little effect. However, the “horns,” which can be as great as 0.20 m in height, appear to be largely ignored by the CUBE algorithm during surface creation, with minimal effect on the final surfaces.7101 Errant PingsErrant or bad pings is evident periodically in the multibeam swath data. This occurred regularly on both 7101 systems. The issue manifests itself as a single ping, or swath, that is skewed (or rolled) from the seafloor at an angle. The cause is unknown, but does not correlate to any spikes in attitude data. These were normally removed manually during swath edit review, resulting in small along-track gaps as viewed in swath editor plan view. However, since only single pings were affected and ping rates were high (generally 10 or more per second), there is no significant detrimental effect on data density. Unrejected errant pings in the dataset may remain, but do not have significant detrimental effect on final surface quality. Sound Speed ErrorA general downward or upward across-track cupping in multibeam data, indicative of sound speed error, is present sporadically in the data set. The sound speed error adversely affected outer beams by up to 0.40 m in places. To minimize the error, sound speed profiles were collected every two hours during multibeam operations, and filters were used in processing to remove the outermost beams. Lines showing more than usual sound speed error received additional filtering, removing soundings greater than 55 degrees from nadir. Extra filtering was more common in the southern most part of the survey area, where sound speed error was worst. Following filtering, the effect of sound speed error on final surfaces normally does not exceeding 0.30 m, and is within specifications.Motion ArtifactMotion artifact is occasionally visible in the final multibeam surfaces. This is the result of uncompensated effects of motion, particularly due to roll. The primary contributer was motion induced on the survey vessels by poor sea states (often 1.5 m or greater), a common and unavoidable condition in this highly exposed area. A survey-grade Applanix POSMV 320 was used for motion compensation, but residual error within the manufacturer specifications for the system remains nonetheless. The problem was addressed in processing by identifying lines with the greatest error and iteratively applying more aggressive outer beam filters, in some instances rejecting beams greater than 55 degrees either side of nadir. No adjustments to line spacing were made in acquisition to compensate for the rejected outer beam data because complete MBES coverage was not required. Following the additional filtering, the effect on the final surface is normally 0.25 m or less, which is within specifications. Note that the ASV-CW5, at 3.5 m in length was a much smaller survey platform than the Q105 at 32 m in length, and therefore, experienced greater induced motion at the same sea states, resulting in more motion artifact for lines run simultaneously.Tide ErrorPeriodic vertical offsets or “busts” is present sporadically in the data set. Tide busts of 0.3 m are relatively common. The south part of the sheet showed the worst tide error, with some busts up to 0.7 m, which exceeds IHO Order 1. Lines run very close in time showed good agreement, but lines at different tidal states showed the worst agreement. Tides are complex in this area and it is apparent the final TCARI model does not fully compensate for tides here, especially in the south portion of the survey as Etolin Strait is entered. However, despite the error, the vast majority of the data is within specifications as indicated in the crossline comparison results.Example tide busts in MBES data in south part of survey area. Separation of up to 0.6 m on adjacent lines.SupportFiles\4_TideBustExample.jpg2 hoursSound speed profiles or "casts" were acquired aboard the Q105 while underway with an Oceanscience RapidCAST system, which utilized a Valeport sound speed profiler. The interval between subsequent casts was normally 2 hours. The sound speed sensor was lowered as close as possible to the seafloor, and then retracted to the vessel and downloaded. When surveying lines covering widely varying water depths, casts were favored in the deeper portions to ensure the entire water column was captured. The ASV-CW5 vessel was not equipped to collect sound speed profiles. Instead, the profile data collected aboard the Q105 was used to correct all ASV-CW5 data. This was possible because the ASV-CW5 worked simultaneously and in close proximity (usually within 200 to 800 m) of the Q105 at all times. Up and down portions of the profiles were averaged and a combined profile at a standardized 0.10 m depth increment was output to CARIS SVP format with time and position. Sound speed profiles were applied with the “nearest in distance within time” method in CARIS HIPS, with time set to two hours. Exceptions, if they occurred, are listed in section B.3 of this report. Refer to the DAPR, section B.2.4 "Data Coverage and Density," for details on the equipment, software, and methodology used to meet object detection, coverage, and data density requirements. Corrections applied to echo soundings are detailed in the project DAPR. No deviations occurred except for those listed below. Note that despite exceptions, affected data is within specifications. Sound speed exception: The following lines were sound speed corrected using nearest in distance within 3 or 4 hours (instead of project standard of 2 hours): ASV-178-D2SS25_-_0003 (3 hours) ASV-178-D2SS25_-_0004 (3 hours) ASV-178-D2SS25_-_0005 (3 hours) ASV-178-D2SS25_-_0002 (4 hours) ASV-178-D2SS25_-_0001 (4 hours) SBET PPK exception: CORS site AB08 was used to process the following line instead of the project base station at Toksook Bay: 0044-Q105-183-D1SS18_-_0001 Calibrations were undertaken as described in the DAPR. No deviations occurred.Multibeam backscatter was logged at all times during this survey, but not processed. Raw DB and XTF files, submitted with the survey deliverables, contain the backscatter records.V5.4 There were no software configuration changes after the DAPR was submitted.H12871_MB_2m_MLLW_FinalCUBE21840NOAA_2mComplete MBESH12871_MB_1m_MLLW_FinalCUBE1020NOAA_1mComplete MBESH12871_SSS_1m_100-D1SSS Mosaic1040N/A100% SSS, block D1, 1st passH12871_SSS_1m_200-D1SSS Mosaic1040N/A100% SSS, block D1, 2nd passH12871_SSS_1m_100-D2SSS Mosaic1040N/A100% SSS, block D2, 1st passH12871_SSS_1m_200-D2SSS Mosaic1040N/A100% SSS, block D2, 2nd passH12871_SSS_1m_100-D3SSS Mosaic1040N/A100% SSS, block D3H12871_SSS_1m_100-D4SSS Mosaic1040N/A100% SSS, block D4, 1st passH12871_SSS_1m_200-D4SSS Mosaic1040N/A100% SSS, block D4, 2nd passThe final depth information for this survey was submitted as two CARIS BASE surfaces (CSAR format) and seven georeferenced SSS mosaic images, which best represented the seafloor at the time of the 2016 survey. The surfaces and images were created from fully processed data with all final corrections applied. As a relatively large survey area, the sheet was broken down into four roughly equivalent sized survey blocks. These were named "D1" in the north, ending with "D4" in the south. MBES Data: The MBES surfaces were created using NOAA CUBE parameters and resolutions in conformance with the 2016 HSSD. Corridor (full coverage) area surfaces were generated in accordance with section 5.2.2.3 (Complete Coverage) while the set-spacing area surface was generated in accordance with section 5.2.2.4 (Set Line Spacing). Surfaces were finalized, and designated soundings were applied, where applicable. Horizontal projection was selected as UTM Zone 3 North, WGS84. Non-finalized versions of the CSAR surfaces are also included. These do not have the _Final designation in the filename. File names for final surfaces was done in accordance with section 8.3.2 (Bathymetric Data) of the 2016 HSSD for MBES data. SSS Data: SSS mosaics were exported from SonarWiz as georeferenced TIFF images at 1 m resolution. These are projected as WGS84 UTM Zone 3N. A world file (TFW) accompanies each TIFF image to provide the georeferencing. SSS filenames are as specified in section 8.2.1, with the addition of an area or block designation at the end of filenames. Singular SSS images for this survey was not practical due to extremely large GeoTIFF file sizes that would result from combined images. Therefore, images were created by survey block, and the block name added as a suffix to the filenames. Note that blocks that received 200% coverage have two 100% coverage TIFFs. Supplementary Data: A CARIS HOB file was submitted (H12871_FFF.HOB) with the survey deliverables as well. The final feature file (FFF) contains meta-data and other data not readily represented by the final surfaces, including bottom samples. A CARIS HOB file containing SSS contacts (H12871_SSS_Contacts.HOB) was also submitted. This file contains significant contacts, if any, found during SSS review. Significant contacts were those identified in the SSS record as having height above the seafloor of 1 m, or greater, in depths less than 20 m, and heights of 10%, or greater, of water depth in depths 20 m and deeper. The 10% allowance is an exception granted for this project by NOAA (see correspondence) to the 5% requirement described in the 2016 HSSD. In this area, contacts were more common in deep water than in shallow water, and this exception was made to limit the number of contacts requiring multibeam development in deeper water, and therefore, facilitate the survey of additional areas over performing multibeam developments. This was considered acceptable given that vessels of 20 m draft are extremely unlikely to attempt transiting this area given its shoal approaches. Note that if an area received complete MBES coverage, contacts were not always identified in the SSS records, nor did they receive additional MBES development. Each object is encoded with mandatory S-57 attributes, additional attributes, and NOAA Extended Attributes (V#5.4).Additional information discussing the vertical or horizontal control for this survey can be found in the accompanying HVCR.Mean Lower Low WaterNelson Island9466298Eastern Nunivak Island9466012Kipnuk9465953Offshore South Nunivak9465683TCARIr300kr2016_rev.tcFinal2016-11-172017-01-26In addition to the subordinate tide station installed to support the project, submerged BMPG (bottom mounted pressure gauges) were also deployed throughout the survey area to capture zoning characteristics. These zoning gauges were used for QC purposes only. All data has been submitted to CO-OPS. A final TCARI grid covering the survey area was issued on January 13th, 2017. However, the grid file was revised and reissued (filename "r300kr2016_rev.tc") on January 26th, 2017. This revised grid "r300kr2016_rev.tc" demonstrated better results in general--though some issues remained--and was applied to all data.WGS84UTM Zone 3NSingle Base0056Toksook BayThe project base continuously logged GPS data at 1 Hz and was utilized to post-process position data in Applanix POSPac MMS software. The Continually Operating Reference Station (CORS) site at Mekoryuk, station ID "AB08," was used for preliminary post-processing in the field, quality control checks for the project base station, and for final positions in rare instances where the project base station experienced outages. All real-time positions for both vessels were replaced in processing with post-processed kinematic (PPK) solutions, with few exceptions (noted where applicable earlier in this report). Quality control confidence checks were performed at least weekly on the survey vessels as well as the base station position. RMS error estimates for positioning results were very good, with RMS error estimated at 0.10 m (or better). Refer to the project DAPR for additional details on quality control checks and results. WAAS was used for real-time corrections in the field, but was replaced in post-processing with the PPK solution, as described in the DAPR. Note: Final positions are WGS84 (instead of NAD83) per Section 2.1 of the 2016 HSSD, which was the governing guidance during the time of field operations.The chart comparison was performed by examining all Raster Navigational Charts (RNCs) and Electronic Navigational Charts (ENCs) that intersect the survey area. The latest editions available at the time of the review (February 10th, 2017) were used. The chart comparison was accomplished by overlaying the finalized BASE surfaces with shoal-biased soundings, and final feature file on the charts in CARIS HIPS. The general agreement between charted soundings and survey soundings was then examined and a more detailed comparison was undertaken for any shoals or other dangerous features. In areas where a large scale chart overlapped with a small scale chart, only the larger scale chart was examined. Results are shown in the following sections. It is recommended that in all cases of disagreement this survey supersede charted data. USCG Notice to Mariners (NM) and USCG Local Notice to Mariners (LNM) were checked for updates affecting the area. None were found that were issued subsequent to issuance date of the project instructions, nor prior to the completion of operations that affect the survey area.1600624111534076372015-122017-01-172017-01-21This survey fully intersects only a small number of charted soundings. Only one agrees within 1 fathom or better. Those with poor agreement are itemized below. 1. Depth in the vicinity of charted 14 fathom sounding at 60-41-31 N, 166-15-10 W was found to be approximately 10.5 fathoms. 2. Depth in the vicinity of charted 9 fathom sounding at 60-35-01 N, 166-01-50 W was found to be approximately 11 fathoms. The charted sounding was not completely covered by this survey. 3. Depth in the vicinity of charted 14 fathom sounding at 60-31-09 N, 165-51-35 W was found to be approximately 14 fathoms. 4. Depth in the vicinity of charted 12 fathom sounding at 60-25-04 N, 165-38-07 W was found to be approximately 14 fathoms. Agreement was also examined for significant trends. None was noted. See included figures show soundings from this survey overlaid on chart 16006. Soundings from the north part of this survey (blue) shown on chart 16006. Soundings are shown in fathoms and feet.SupportFiles\7_H12871_ChartCompare-N.jpgSoundings from the south part of this survey (blue) shown on chart 16006. Soundings are shown in fathoms and feet.SupportFiles\8_H12871_ChartCompare-S.jpgUS2AK95M153407642016-08-292016-08-29falseThe same differences observed for the RNC apply to the ENC.No maritime boundary points were assigned for this survey.There are no charted features labeled PA, ED, PD, or Rep. within the survey extents. PD soundings are charted nearby but investigation was not required.No uncharted features were found during this survey.1H12871_DTON_Sounding2016-08-30One DTON report was made for this survey. A sounding was submitted as a DTON with a depth of 9.08 m (5 fathoms) at 60-39-23.0 N, 166-11-40.6 W. Previously, no data existed on chart 16006 in the immediate vicinity, but the nearest charted depth to the north suggested a depth of 14 fathoms for the area. The DTON is now accurately reflected on the chart. Note that the DTON sounding depth was submitted using preliminary corrections. Depth at the DTON locations may differ slightly due to the application of final correctors, including final tides. Correspondence relating to DTONs as well as DTON reports can be found in Appendix II. Submitted DTONs are included in the FFF for reference. No shoals or potentially hazardous features were found with the exception of the DTON discussed previously.No channels exist in the survey area.Bottom samples were collected for this survey. 10 samples were assigned. A sample was successfully obtained at all 10 positions. Samples returned primarily fine brown sand in the north, grading into mud and black rock in the south. Samples were not retained. However, photos were taken of most samples prior to discarding. Bottom characteristics were encoded as SBDARE objects in the FFF, with any applicable photos in the accompanying "multimedia" directory, included with the survey deliverables.Shoreline investigation was not required, and the area did not intersect shoreline.Comparison with prior surveys was not required. However, Junction analysis, described previously in this report, was undertaken for overlapping contemporary surveys.No ATONs were assigned, nor did any fall within the survey extents.No overhead features existed within the survey area.There are no submarine features of special note.Ferry routes and terminals do not exist within the survey area.Platforms do not exist within the survey area.Any significant features and conditions encountered have been described previously.No construction or dredging was occurring within the survey extents, nor are there any known future plans for construction or dredging in the survey area.No new surveys are recommended in this area.No new chart insets are recommended in this area.Field operations contributing to the completion of survey H12871 were conducted under my direct supervision with frequent personal checks of progress, integrity, and adequacy.This report, digital data, and all other accompanying records are approved. All records are respectfully submitted and forwarded for final review.The survey data was collected in accordance with the project Work Instructions and Statement of Work, and meets or exceeds the requirements set in the 2016 NOS Hydrographic Surveys and Specifications Deliverables (HSSD) document. This data is adequate to supersede charted data in common areas. This survey is complete and no additional work is required with the exception of any deficiencies, if any, noted in this Descriptive Report. The Data Acquisition and Processing Report (DAPR) and Horizontal and Vertical Control Report (HVCR) were submitted concurrently with this report and the survey deliverables. Other significant required reports or data packages submitted separately are listed below.Andrew Orthmann, C.H.TerraSond Charting Program Manager2017-03-06Coast Pilot Review (OPR-R300-KR-16_Coast Pilot Review Report)2017-02-13NCEI Sound Speed Data2016-12-20Trained Marine Mammal Observers Logsheet2016-11-21Marine Mammal Observation Logs2016-11-17Tides and Water Levels Package and Reports (one for each project tide station)2016-10-21