Orthomosaic imagery for Whiskeytown Lake and surrounding area, northern California, 2020-11-10

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Frequently anticipated questions:


What does this data set describe?

Title:
Orthomosaic imagery for Whiskeytown Lake and surrounding area, northern California, 2020-11-10
Abstract:
This portion of the data release presents an RGB orthomosaic image of Whiskeytown Lake and the surrounding area derived from Structure from Motion (SfM) processing of aerial imagery acquired on 2020-11-10. The orthomosaic is available in a high-resolution 5-centimeter (cm) version, as well as a medium-resolution 25 cm version. The high-resolution version is divided into two tiles (east and west) to reduce file download sizes. All imagery is provided in a three-band cloud optimized GeoTIFF format, with 8-bit unsigned integer values compressed using high-quality JPEG compression. The raw imagery used to create the orthomosaic image was acquired from a manned aircraft on 2020-11-10. The acquisition flight was conducted by The 111th Group Aerial Photography, using a Hasselblad A6D-100c camera. The imagery was acquired from an approximate altitude of 880 meters (2,900 feet) above ground level, to produce a nominal ground sample distance (pixel size) of 5 centimeters (2 inches). An onboard dual-frequency GPS receiver was used to record the precise time and position of each image. Coordinates for ground control points consisting of photo-identifiable objects were measured independently using survey-grade post-processed kinematic (PPK) GPS.
Supplemental_Information:
Additional information about the field activities from which these data were derived is available online at:
http://cmgds.marine.usgs.gov/fan_info.php?fan=2020-627-FA
Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Data used in creating this DSM were collected under the Department of the Interior, National Park Service Scientific Research and Collecting Permit WHIS-2018-SCI-0023, WHIS-2019-SCI-0011 and WHIS-2020-SCI-0006.
  1. How might this data set be cited?
    Logan, Joshua B., East, Amy E., and Ritchie, Andrew C., 20210702, Orthomosaic imagery for Whiskeytown Lake and surrounding area, northern California, 2020-11-10: data release DOI:10.5066/P9HEDYNT, U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, California.

    Online Links:

    This is part of the following larger work.

    Logan, Joshua B., Dartnell, Peter, East, Amy E., and Ritchie, Andrew C., 20200527, Bathymetry, topography and orthomosaic imagery for Whiskeytown Lake, northern California: data release DOI:10.5066/P9HEDYNT, U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, CA.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -122.63548
    East_Bounding_Coordinate: -122.51091
    North_Bounding_Coordinate: 40.66341
    South_Bounding_Coordinate: 40.58915
  3. What does it look like?
    https://www.sciencebase.gov/catalog/file/get/605259bfd34e7eb1cb3eb49f?name=Whiskeytown_2020-11-10_orthomosaic_browse.png (PNG)
    RGB orthomosaic image from 2020-11-10.
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 10-Nov-2020
    Ending_Date: 10-Nov-2020
    Currentness_Reference:
    ground condition at time data were collected
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: GeoTIFF
  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.
    2. What coordinate system is used to represent geographic features?
      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 10
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -123.00000
      Latitude_of_Projection_Origin: 0.00000
      False_Easting: 500000.0
      False_Northing: 0.00
      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.250
      Ordinates (y-coordinates) are specified to the nearest 0.250
      Planar coordinates are specified in Meters
      The horizontal datum used is North American Datum of 1983, 2011 realization (NAD83(2011))..
      The ellipsoid used is GRS 1980.
      The semi-major axis of the ellipsoid used is 6378137.00.
      The flattening of the ellipsoid used is 1/298.257222101.
  7. How does the data set describe geographic features?
    GeoTIFF
    GeoTIFF containing RGB color bands. (Source: Producer defined)
    Band_1
    Red band (Source: Producer defined)
    Range of values
    Minimum:0
    Maximum:255
    Band_2
    Green band (Source: Producer defined)
    Range of values
    Minimum:0
    Maximum:255
    Band_3
    Blue band (Source: Producer defined)
    Range of values
    Minimum:0
    Maximum:255

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Joshua B. Logan
    • Amy E. East
    • Andrew C. Ritchie
  2. Who also contributed to the data set?
    Data collection was funded by the U.S. Geological Survey. Data acquisition was conducted by The 111th Group Aerial Photography. Data processing was done by the 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

    831-427-4747 (voice)
    pcmsc_data@usgs.gov

Why was the data set created?

This RGB orthomosaic image was created to help evaluate the initial post-fire conditions on the exposed margins of Whiskeytown Lake as well as the exposed, unvegetated portions of the surrounding watersheds. It is intended for use by scientists, managers, and the general public. The orthomosaic can be used with geographic information systems (GIS) software for research purposes.

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: 10-Nov-2020 (process 1 of 5)
    Aerial imagery was collected by the 111th Group, Inc. on 2020-11-10 between 20:49 and 22:10 Universal Coordinated Time (UTC) (12:49 to 14:10 Pacific Standard Time (PST)), using a Hasselblad A6D-100c mounted in a nadir orientation. The imagery was acquired from an approximate altitude of 890 meters (2,920 feet) above ground level, to produce a nominal ground sample distance (pixel size) of 5 centimeters (2 inches). A total of 1,283 images were acquired in the survey area, with an approximate 70 percent along-line image overlap (forelap) and 50 percent side-to-side overlap (sidelap). An onboard dual-frequency GPS receiver was used to record the precise shutter time and position of each image. Person who carried out this activity:
    Patrick Belanger
    The 111th Group Inc
    13025 Murphy Ave. Suite 100
    San Martin, CA

    408-683-9111 (voice)
    pat@the111th.com
    Date: 2020 (process 2 of 5)
    The GPS data from the aircraft onboard dual-frequency GPS was post processed using Precise Point Positioning (PPP) in the Novatel GrafNav GNSS post-processing software package. Precise positions for camera shutter event marks were interpolated using the Grafnav Camera Event Mark tool and exported in NAD83(2011) spherical and projected coordinates. Person who carried out this activity:
    Joshua Logan
    U.S. Geological Survey, Pacific Coastal and Marine Science Center
    2885 Mission Street
    Santa Cruz, CA

    831-460-7519 (voice)
    jlogan@usgs.gov
    Date: 2020 (process 3 of 5)
    Ground control was established by measuring the positions of approximately 84 photo-identifiable marks or objects using survey-grade post-processed-kinematic (PPK) GPS equipment. All measurements were referenced to a static base station operating on a temporary benchmark within the survey area. The position of the base station was established using the National Geodetic Survey Online Positioning User Service (OPUS). Person who carried out this activity:
    Joshua Logan
    U.S. Geological Survey, Pacific Coastal and Marine Science Center
    2885 Mission Street
    Santa Cruz, CA

    831-460-7519 (voice)
    jlogan@usgs.gov
    Date: 2020 (process 4 of 5)
    Imagery from the raw Hasselblad 3FR format was converted to Hasselblad FFF format using the Hassleblad Phocus software package. The imagery exposure value (EV) was increased by +0.25 stops, and the chromatic aberration and vignetting corrections were applied under the Lens Correction tab. The distortion correction was not applied. The resulting adjusted images were exported using the JPG Max profile (JPG with Quality set to Maximum). Person who carried out this activity:
    Joshua Logan
    U.S. Geological Survey, Pacific Coastal and Marine Science Center
    2885 Mission Street
    Santa Cruz, CA

    831-460-7519 (voice)
    jlogan@usgs.gov
    Date: 2020 (process 5 of 5)
    Structure from Motion (SfM) processing techniques were used to create the Digital Surface Model and Orthomosaic in the Agisoft Photoscan/Metashape software package using the following work flow: 1. The aerial imagery was loaded into Agisoft, and the camera positions were updated using the PPP post-processed onboard GPS data. 2. Initial image alignment was performed with the following parameters - Accuracy: 'high'; Pair selection: 'reference', 'generic'; Key point limit: 0 (unlimited); Tie point limit: 0 (unlimited). 3. Optimization and lens calibration parameters f, cx, cy, k1, k2, k3, p1, and p2 were included. 4. Ground control points (GCPs) previously measured with PPK GPS were manually identified and placed in the imagery. 5. Sparse point cloud error reduction was performed using an iterative gradual selection and camera optimization process with the following parameters: Reconstruction Uncertainty: 10; Projection Accuracy: 3; Reconstruction Error: 0.3. 6. A dense point cloud was created using the 'high' accuracy setting, with 'aggressive' depth filtering. 7. An initial Digital Surface Model (DSM) with a native resolution of 0.096 meters per pixel was created using points from the dense point cloud. An exterior boundary was digitized and used as a clipping mask to exclude obvious edge artifacts and large areas of interpolation. The DSM was exported to a GeoTIFF format with a 0.250-meter pixel resolution. 8. An RGB orthomosaic with a native resolution of 0.048 meters per pixel was created using the DSM as the orthorectification surface. The orthomosaic was exported to a GeoTIFF format at two resolutions: 0.050-meter pixels, and 0.250-meter pixels. 9. The RGB orthomosaic was converted to a cloud optimized GeoTIFF format for compatibility with cloud storage services using the GDAL software package. The orthomosaic was scaled to byte values and compressed using JPEG compression, with a quality of 90. The higher-resolution orthomosaic was divided into an east and west tile to reduce the file size, while the lower-resolution version was kept as one file. Person who carried out this activity:
    Joshua Logan
    U.S. Geological Survey, Pacific Coastal and Marine Science Center
    2885 Mission Street
    Santa Cruz, CA

    831-460-7519 (voice)
    jlogan@usgs.gov
  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?
    No formal attribute accuracy tests were conducted.
  2. How accurate are the geographic locations?
    Horizontal positional accuracy was evaluated by comparing the positions of 24 independent photo-identifiable ground control check points measured with survey-grade post-processed kinematic (PPK) GPS with their estimated positions derived from the structure from motion (SfM) processing workflow. The root-mean-square error (RMSE) of the residual values of the measured positions versus the SfM-estimated positions was 0.070 meters. It should be noted that this estimate is for unvegetated, bare ground areas only. Additional sources of error such as noise or blurriness within the source imagery, poor terrain reconstruction in areas of uniform color and texture such as roads and parking lots, poor terrain reconstruction on small islands surrounded by water, and vegetation artifacts may cause additional errors in portions of the DSM which likely exceed the stated uncertainty bounds.
  3. How accurate are the heights or depths?
    Vertical positional accuracy was not evaluated for this data product.
  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?
    No formal logical accuracy tests were conducted.

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(s) 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? The RGB orthomosaic images are available as Cloud Optimized GeoTIFF files in two resolutions. High resolution 5 cm (Whiskeytown_2020-11-10_orthomosaic_5cm _east.tif and Whiskeytown_2020-11-10_orthomosaic_5cm_west.tif), and medium resolution 25 cm (Whiskeytown_2020-11-10_orthomosaic_25cm.tif).
  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?
  5. What hardware or software do I need in order to use the data set?
    These data can be viewed with GIS software or other software capable of displaying geospatial raster data.

Who wrote the metadata?

Dates:
Last modified: 02-Jul-2021
Metadata author:
U.S. Geological Survey, Pacific Coastal and Marine Science Center
Attn: PCMSC Science Data Coordinator
2885 Mission Street
Santa Cruz, CA

831-427-4747 (voice)
pcmsc_data@usgs.gov
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

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