Structure-from-Motion (SfM) surface models derived from seafloor video from the Channel Islands, California

Frequently anticipated questions:

• What does this data set describe?
  1. How might this data set be cited?
  2. What geographic area does the data set cover?
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
  5. What is the general form of this data set?
  6. How does the data set represent geographic features?
  7. How does the data set describe geographic features?
• Who produced the data set?
  1. Who are the originators of the data set?
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
• Why was the data set created?
• How was the data set created?
  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
  3. What similar or related data should the user be aware of?
• How reliable are the data; what problems remain in the data set?
  1. How well have the observations been checked?
  2. How accurate are the geographic locations?
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
  5. How consistent are the relationships among the data, including topology?
• How can someone get a copy of the data set?
  1. Are there legal restrictions on access or use of the data?
  2. Who distributes the data?
  3. What's the catalog number I need to order this data set?
  4. What legal disclaimers am I supposed to read?
  5. How can I download or order the data?
• Who wrote the metadata?

What does this data set describe?

1. How might this data set be cited?
   Dailey, Evan T., 2018, Structure-from-Motion (SfM) surface models derived from seafloor video from the Channel Islands, California: data release DOI:10.5066/P929SXZE, U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, California.

   Online Links:

   • https://doi.org/10.5066/P929SXZE
   • https://www.sciencebase.gov/catalog/file/get/5bae6310e4b08583a5d30f7c

2. What geographic area does the data set cover?

   West_Bounding_Coordinate: -120.275
   East_Bounding_Coordinate: -120.27
   North_Bounding_Coordinate: 34.011
   South_Bounding_Coordinate: 34.009
   

3. What does it look like?

   https://www.sciencebase.gov/catalog/file/get/5bae6310e4b08583a5d30f7c?name=SfM_AutoCal-ShipGPS_vert.png&allowOpen=true (PNG)

   Image map of the SfM elevation model created using automatic calibration and shipboard GPS locations

4. Does the data set describe conditions during a particular time period?

   Beginning_Date: 25-Sep-2016

   Ending_Date: 29-Sep-2016

   Currentness_Reference:

   ground condition

5. What is the general form of this data set?

   Geospatial_Data_Presentation_Form: TIFF
   

6. How does the data set represent geographic features?
   1. How are geographic features stored in the data set?
      This is a Raster data set. It contains the following raster data types:
      • Dimensions, type Grid Cell
   2. What coordinate system is used to represent geographic features?
      

      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:

      UTM_Zone_Number: 10N
      Transverse_Mercator:

      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -123.0
      Latitude_of_Projection_Origin: 0.0
      False_Easting: 500000.0
      False_Northing: 0.0
      

      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.00422002
      Ordinates (y-coordinates) are specified to the nearest 0.00422002
      Planar coordinates are specified in METERS
      The horizontal datum used is WGS_1984_UTM_Zone_10N.
      The ellipsoid used is WGS 84.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257223563.
      

      Vertical_Coordinate_System_Definition:

      Altitude_System_Definition:

      Altitude_Datum_Name: MLLW
      Altitude_Resolution: 1.0E-4
      Altitude_Distance_Units: Meters
      Altitude_Encoding_Method:

      Explicit elevation coordinate included with horizontal coordinates

7. How does the data set describe geographic features?

   Attribute table

   Table containing attribute information associated with the dataset (Source: U.S. Geological Survey)

   Value

   Depth relative to mean lower low water (MLLW) in meters (Source: U.S. Geological Survey)

   Range of values
   Minimum:	-28.6
   Maximum:	-36.0457
   Units:	Meters

Who produced the data set?

1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
   • Evan T. Dailey
2. Who also contributed to the data set?

   Data collection was funded by U.S. Geological Survey

3. To whom should users address questions about the data?
   U.S. Geological Survey, Pacific Coastal and Marine Science Center

   Attn: PCMSC Science Data Coordinator

   2885 Mission Street

   Santa Cruz, CA
   

   831-460-4747 (voice)

   pcmsc_data@usgs.gov

Why was the data set created?

These surface models were produced to assess the accuracy and precision of different Structure-from-Motion workflows.

How was the data set created?

1. From what previous works were the data drawn?
2. How were the data generated, processed, and modified?

   Date: Jan-2018 (process 1 of 3)

   Data Collection: Video was collected during USGS field activity 2016-668-FA in the Channel Islands, CA. Video footage was collected using the USGS camera sled, which was equipped with two high resolution video cameras, one pointing downward (vertical) and the other pointing slightly forward (oblique) and was towed by the research vessel Shearwater. The camera sled was also equipped with paired lasers to provide scaling to features on the seafloor. Video was recorded in depths approximately 10 to 70 meters. Shipboard GPS locations were recorded every 1 second into one of the audio channels of the video using Red Hen Systems, LLC hardware.

   Date: 08-Jan-2018 (process 2 of 3)

   Structure-from-Motion Processing: Still frames were extracted from the video at a constant rate of 1 frame every 2/3 second. For the shipboard GPS method 6 markers were selected throughout the video imagery. Those markers were assigned latitude and longitude values from the shipboard GPS according to the playback time of that video frame, and the markers were assigned the depth from the existing sonar that corresponded to that location. For the georeferencing method, features visible in the video imagery were georeferenced to that feature where it was visible in the sonar data (7 markers were assigned this way). A lens model was developed using the BOBSled cameras to record imagery of a calibration board in a salt-water tank. That imagery was used to create a model, and the SfM software's lens model was exported as the fixed lens model. Automatic calibration by the SfM software was also used. Four models were produced: calibrated using a fixed lens model with the shipboard GPS that was embedded in the audio ("SfM_Cal-ShipGPS_UTM10N.tif"), lens model auto-calibrated by the SfM software with ship GPS ("SfM_AutoCal-ShipGPS_UTM10N.tif"), calibrated using a fixed lens model with locations derived from georeferencing the video imagery to the existing sonar bathymetry ("SfM_Cal-Georef_UTM10N.tif"), and auto-calibrated with georeferenced locations ("SfM_AutoCal-Georef_UTM10N.tif"). SfM models were created using Agisoft PhotoScan version 1.3.5. Photos were aligned in PhotoScan, iteratively 'cleaned' to reduce error using the following steps in PhotosScan: all points with reconstruction uncertainty greater than 10 were deleted (iteratively - no more than 50 percent of the models points were deleted at a time); all points with projection accuracy greater than 3 were deleted; reprojection error was reduced to 0.3 by iteratively deleting no more than 10 percent of the models points; after each of the previous steps, cameras were optimized; a dense point cloud was created in PhotoScan; digital elevation model created from dense point cloud in PhotoScan; elevation model exported as TIF image.

   Date: 19-Oct-2020 (process 3 of 3)

   Edited metadata to add keywords section with USGS persistent identifier as theme keyword. No data were changed. Person who carried out this activity:
   

   U.S. Geological Survey

   Attn: VeeAnn A. Cross

   Marine Geologist

   384 Woods Hole Road

   Woods Hole, MA
   

   508-548-8700 x2251 (voice)

   508-457-2310 (FAX)

   vatnipp@usgs.gov

3. What similar or related data should the user be aware of?
   Cochrane, Guy R., Finlayson, David P., and Dailey, Evan T., 2018, Bathymetry data collected in 2007 from the San Miguel Passage in the Channel Islands, California: data release DOI:10.5066/F78G8HVC, U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, CA.

   Online Links:

   • https://doi.org/10.5066/F78G8HVC

   Golden, Nadine E., Ackerman, Seth D., and Dailey, Evan T., 2015, Coastal and Marine Geology Program video and photograph portal: data release DOI:10.5066/F7JH3J7N, U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, CA.

   Online Links:

   • https://doi.org/10.5066/F7JH3J7N

How reliable are the data; what problems remain in the data set?

1. How well have the observations been checked?
   The horizontal and vertical accuracies of the surface models were compared against existing sonar data (Cochrane and others, 2018). The scale accuracy of the surface models was compared by measuring the camera sled's scale laser as it appeared in the original still frames and the still frames after being aligned and located in the SfM software.
2. How accurate are the geographic locations?
   Assessing the true horizontal accuracy of the models is prone to uncertainty because they were compared against lower-resolution sonar data. The sonar data had a horizontal accuracy of no less than 2 m. The horizontal accuracy of the SfM models ranged from approximately 0 to 5 m as compared to the sonar data. Overall horizontal accuracy is assumed to be no less than 2 m and no greater than 10 m. The average horizontal scaling of all the models is estimated to be accurate to within 1.25 cm, and 0.15 on average in the model created using shipboard GPS and automatic calibration.
3. How accurate are the heights or depths?
   Estimated to be 0.6 meters different than the sonar data, on average. The sonar data had a vertical accuracy estimated to be no less than 5 percent water depth. The average vertical scaling of all the models is estimated to be accurate to within 1.25 cm, and 0.15 on average in the model created using shipboard GPS and automatic calibration.
4. Where are the gaps in the data? What is missing?
   Dataset is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details.
5. How consistent are the relationships among the observations, including topology?
   All data fall within expected ranges.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints: None
Use_Constraints:

USGS-authored or produced data and information are in the public domain from the U.S. Government and are freely redistributable with proper metadata and source attribution. Please recognize and acknowledge the U.S. Geological Survey as the originator of the dataset and in products derived from these data. This information is not intended for navigation purposes.

1. Who distributes the data set? (Distributor 1 of 1)
   
   U.S. Geological Survey - ScienceBase

   Denver Federal Center, Building 810, Mail Stop 302

   Denver, CO
   

   1-888-275-8747 (voice)

   sciencebase@usgs.gov
2. What's the catalog number I need to order this data set? These data are available in TIFF format (SfM_AutoCal-Georef_UTM10N.tif, SfM_Cal-Georef_UTM10N.tif, SfM_AutoCal-ShipGPS_UTM10N.tif, SfM_Cal-ShipGPS_UTM10N.tif) contained in a single zip file which also includes CSDGM FGDC-compliant metadata, and a browse image map of the data (.jpg). The TIFF data files are named with the following convention: SfM, calibration method, location method, and projected coordinate system.
3. What legal disclaimers am I supposed to read?

   Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty.

4. How can I download or order the data?
   • Availability in digital form:

     Data format:	The .zip file contains four TIFF rasters (.tif), a browse image map, and the metadata. in format TIFF (version Agisoft PhotoScan Professional Version 1.3.5 build 5649 (64 bit)) Size: 1264.68
     Network links:	https://www.sciencebase.gov/catalog/file/get/5bae6310e4b08583a5d30f7c https://doi.org/10.5066/P929SXZE

   • Cost to order the data: None.

5. What hardware or software do I need in order to use the data set?

   These data can be viewed with Esri ArcGIS software.

Who wrote the metadata?

Dates:

Last modified: 19-Oct-2020

Metadata author:

U.S. Geological Survey, Pacific Coastal and Marine Science Center

Attn: PCMSC Science Data Coordinator

2885 Mission Street

Santa Cruz, CA

831-460-4747 (voice)

pcmsc_data@usgs.gov

Metadata standard:

Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)