Process_Description:
Aerial imagery was collected using a Department of Interior-owned quadcopter fitted with Ricoh GR II digital cameras featuring global shutters. The camera was mounted using fixed mount on the bottom of the UAS and oriented in an approximately nadir orientation. During acquisition the UAS was flown on pre-programmed autonomous flight lines at an approximate altitude of 110 meters above ground level (AGL), resulting in a nominal ground-sample-distance (GSD) of 2.9 centimeters per pixel. The flight lines were spaced to provide approximately 70-80 percent overlap between images from adjacent lines. Terrain-following was used to maintain a somewhat consistent height above the ground, as the UAS flew over terrain of increasing elevation away from the takeoff location. The camera was triggered at 1 Hz using an external intervalometer. Before each flight, the camera’s digital ISO, aperture and shutter speed were manually set to adjust for ambient light conditions. Although these settings were changed between flights, they were not permitted to change during a flight; thus, the images from each flight were acquired with consistent camera settings. The images were recorded in raw Adobe DNG format.
Process_Date: 20240430
Process_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Joshua Logan
Contact_Organization:
U.S. Geological Survey, Pacific Coastal and Marine Science Center
Contact_Position: Physical Scientist
Contact_Address:
Address_Type: mailing address
Address: 2885 Mission Street
City: Santa Cruz
State_or_Province: CA
Postal_Code: 95060
Country: US
Contact_Voice_Telephone: 831-460-7519
Contact_Facsimile_Telephone: 831-427-4748
Contact_Electronic_Mail_Address: jlogan@usgs.gov
Process_Description:
Ground control was established using ground control points (GCPs) consisting of a combination of small square tarps with black-and-white cross patterns and temporary "X" marks placed with chalk on the ground surface throughout the survey area before the flight. The GCP positions were measured using real-time kinematic (RTK) GPS, using corrections from a GPS base station located on a temporary benchmark ("SFKW") established on the foot of the debris flow, near the takeoff site. The approximate base station position was initially derived using an autonomous position. The final coordinates for SFKW were derived using a seven-hour static occupation, submitted to the National Geodetic Survey Online User Positioning Service (OPUS-S), conforming to the criteria for a Level II single-base OPUS-S survey according to USGS Techniques and Methods 11-D1. For each GCP measurement the GPS receiver was placed on a fixed-height tripod and set to occupy the GCP for a minimum occupation time of one minute. After the survey was completed, the RTK data were updated using the final SFKW position using the Trimble Business Center software package.
Process_Date: 2024
Process_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Joshua Logan
Contact_Organization:
U.S. Geological Survey, Pacific Coastal and Marine Science Center
Contact_Address:
Address_Type: mailing and physical
Address: 2885 Mission Street
City: Santa Cruz
State_or_Province: CA
Postal_Code: 95060
Contact_Voice_Telephone: 831-460-7519
Contact_Electronic_Mail_Address: jlogan@usgs.gov
Process_Description:
The image files were renamed using a custom python script. The file names were formed using the following pattern Fx-YYYYMMDDThhmmssZ_Ryz.*, where:
- Fx = Flight number
- YYYYMMDDThhmmssZ = date and time in the ISO 8601 standard, where 'T' separates the date from the time, and 'Z' denotes UTC ('Zulu') time.
- Ry = RA or RB to distinguish camera 'RicohA' from 'RicohB'
- z = original image name assigned by camera during acquisition
- * = file extension (JPG or DNG)
The approximate image acquisition coordinates were added to the image metadata (EXIF) ('geotagged') using the image timestamp and the telemetry logs from the UAS onboard single-frequency 1-Hz autonomous GPS. The geotagging process was done using the exiftool utility via the command line. To improve timestamp accuracy, the camera time was set to coordinated UTC time using a smart phone wireless connection to the camera. The positions stored in the EXIF are in geographic coordinates referenced to the WGS84(G1150) coordinate reference system (EPSG:4979), with elevation in meters relative to the WGS84 ellipsoid.
Additional pertinent metadata were added to the EXIF headers using the command-line 'exiftool' software.
The Adobe Camera RAW software package was used to adjust the exposure value (EV) of the DNG images. For the image from flight F01, the EV was increased by an EV of +2.0; for flight F02, the EV was increased by an EV of +2.7. The images were exported in TIFF format, and JPG format with a quality setting of 93.
Process_Date: 2024
Process_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Joshua Logan
Contact_Organization:
U.S. Geological Survey, Pacific Coastal and Marine Science Center
Contact_Address:
Address_Type: mailing and physical
Address: 2885 Mission Street
City: Santa Cruz
State_or_Province: CA
Postal_Code: 95060
Contact_Voice_Telephone: 831-460-7519
Contact_Electronic_Mail_Address: jlogan@usgs.gov
Process_Description:
Structure-from-motion (SfM) processing techniques were used to create point clouds, DSMs, and orthomosaic images in the Agisoft Photoscan/Metashape software package using the following workflow:
1. Image alignment was performed using the TIFF images, and the following parameters:
Accuracy: 'high'
Pair selection: 'reference', 'generic'
Key point limit: 40,000
Tie point limit: 4,000
2. Ground control point (GCP) positions were imported, and markers were manually identified and placed in the images.
3. Sparse point cloud error reduction was performed using an automated python script (Logan and others, 2022), to sequentially apply the Reconstruction Uncertainty and Projection Accuracy gradual selection filters to remove 50 percent of the sparse points, followed by camera optimization. This resulted in the following final gradual selection filter values:
Final Reconstruction Uncertainty: 26.7
Final Projection Accuracy: 3.0
Lens calibration parameters for optimization: f, cx, cy, k1, k2, k3, p1, and p2
4. Additional sparse point cloud error reduction was performed using the automated python script to iteratively apply the Reprojection Error gradual selection filter and camera optimization such that no more than 10 percent of the remaining sparse points are deleted at a time. Between each iteration of the filter, camera optimization was performed with the following lens calibration parameters: f, cx, cy, k1, k2, k3, p1, and p2. Once Reprojection Error was reduced below 1 pixel, additional lens calibration parameters (k4, b1, b2, p3, and p4) were included during optimization. This process was repeated until the following final Reprojection Error filter levels were achieved:
Final Reprojection Error: 0.3
Lens calibration parameters for optimization: f, b1, b2, cx, cy, k1, k2, k3, k4, p1, p2, p3 and p4
Additional remaining sparse points obviously above or below the true surface were manually deleted after the last error reduction iteration, and a final optimization was performed.
5. A dense point cloud was created using the 'high' accuracy setting, with 'aggressive' depth filtering, and 'confidence' calculated. Points with confidence less than 3 were assigned a classification value of 7 (noise).
6. A Digital Surface Model (DSM) was created using all points in the dense point cloud. The DSM was exported to a GeoTIFF file with 10-centimeter pixel resolution and Lempel-Ziv-Welch (LZW) compression. The raster cell origin was set to an integer value to ensure horizontal raster alignment with other data products.
7. A orthomosaic image was created using the DSM as a rectification surface.
8. A clipping mask was manually digitized to exclude areas outside of the area of interest.
9. Data products were exported, using the clipping mask to exclude areas outside of the area of interest. The point cloud was exported to a cloud-optimized point cloud (COPC LAZ) file. The DSM was exported to a GeoTIFF file with 10-centimeter pixel resolutions and LZW compression. The orthomosaic was exported to a GeoTIFF file with a 3-cm pixel resolution. The raster cell origins of both raster products were set to integer values to ensure horizontal raster alignment with other geospatial data.
10. The GDAL "gdal_translate" utility was used to convert the DSM GeoTIFF file to a cloud-optimized GeoTIFF, with statistics calculated and "DEFLATE" compression applied.
11. The GDAL "gdal_translate" utility was used to convert the orthomosaic GeoTIFF to a cloud-optimized GeoTIFF, with "JPG" compression applied with a quality level of 90.
Process_Date: 2024
Process_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Joshua Logan
Contact_Organization:
U.S. Geological Survey, Pacific Coastal and Marine Science Center
Contact_Position: Physical Scientist
Contact_Address:
Address_Type: mailing address
Address: 2885 Mission Street
City: Santa Cruz
State_or_Province: CA
Postal_Code: 95060
Country: US
Contact_Voice_Telephone: 831-460-7519
Contact_Facsimile_Telephone: 831-427-4748
Contact_Electronic_Mail_Address: jlogan@usgs.gov
