Attribute_Accuracy_Report:
The accuracy of the position data is based on the accuracy and precision of the GNSS equipment and camera timing, number and length of baselines and atmospheric conditions.
Note that the positions in the imagery headers are aircraft GNSS antenna positions and are limited to six decimal places, whereas the positions in the external navigation file are accurate to ten decimal places and are therefore highly recommended for use in SfM processing to produce the highest quality derived products.
No effort is made to optimize exposure through post-processing. These data represent raw imagery, as collected, and subsequently used in SfM photogrammetric processing workflows.
All data fall within expected ranges.
RGB (red, green, blue) values are 8-bits per band, generally not saturated or underexposed. In a few cases of high or low light conditions, some imagery may be over or underexposed.
GNSS values are checked for consistency and outliers. Bad data are discarded, and missing data are interpolated.
This dataset is considered complete for the information presented, as described in the abstract. Users are advised to read the entire metadata record carefully and to examine the imagery header metadata for additional details. Some images may lack position information in their imagery headers resulting from a momentary disruption in GNSS signals but in most cases, interpolated positions based on GNSS timestamps were applied to these images. The beginning and end of the survey were reviewed to cull extraneous images such as camera testing or inadvertently triggered image.
Process_Step:
Process_Description:
IMAGE & POSITION ACQUISITION -- C. W. Wright Consulting used the Precision Airborne Camera (PAC) system, equipped with a Sony A7R 36 Megapixel digital camera aboard a Piper P28A aircraft to conduct a nadir (vertical) aerial imagery survey from Cape Lookout to Corolla, North Carolina on August 2, 2020, to document pre-storm conditions before the passage of Hurricane Isaias on August 3, 2020. Data were collected to facilitate SfM processing (Westoby and others, 2012) in shore-parallel lines, flying at approximately 50 meters per second (m/s) and capturing true color imagery at 1 Hz, resulting in image footprints with approximately 75-80% endlap, 60-70% sidelap, and 5.3-cm GSD. Raw (ARW) images, raw dual-frequency carrier phase GNSS data, and photo event time data were delivered to the USGS St. Petersburg Coastal and Marine Science Center (SPCMSC).
Process_Date: 20200802
Process_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Christine J. Kranenburg
Contact_Organization:
U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center
Contact_Position: Cartographer
Contact_Address:
Address_Type: Physical and Mailing
Address: 600 4th Street South
City: St. Petersburg
State_or_Province: FL
Postal_Code: 33701
Country: USA
Contact_Voice_Telephone: 727-502-8000
Contact_Electronic_Mail_Address: ckranenburg@usgs.gov
Process_Step:
Process_Description:
IMAGE RENAMING -- Images received from the vendor (in raw image file format, ARW) were renamed using IrfanView software to conform to the following naming convention: yyyy-mmdd-hhmmss-DSCnnnnn-N7251F.ARW, where yyyy_mmdd represents the year (yyyy), month (mm) and day (dd) of capture; hhmmss is the time of capture as hours (hh), minutes (mm), seconds(ss) in Universal Coordinated Time (UTC); DSCnnnnn represents a sequential image identifier (ID) generated by the camera; and N7251F is the tail number of the aircraft used for acquisition. The following pattern string is used in the batch renaming tool to rename the images from their raw name format (DSCnnnnn) to the naming convention defined above: $E36868(%Y-%m%d-%H%M%S)-$N-N7251F.
Process_Date: 20200803
Process_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Christine J. Kranenburg
Contact_Organization:
U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center
Contact_Position: Cartographer
Contact_Address:
Address_Type: Physical and Mailing
Address: 600 4th Street South
City: St. Petersburg
State_or_Province: FL
Postal_Code: 33701
Country: USA
Contact_Voice_Telephone: 727-502-8000
Contact_Electronic_Mail_Address: ckranenburg@usgs.gov
Process_Step:
Process_Description:
IMAGE CONVERSION -- Renamed images were batch-converted to a format compatible with photogrammetry processing software using Adobe Photoshop Camera Raw and applying the Camera Neutral Profile (Joint Photographic Experts Group format, JPEG). Software versions, conversion date, and other parameters are recorded in individual imagery header metadata.
Process_Date: 20200813
Process_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Andrew R. Ritchie
Contact_Organization:
U.S. Geological Survey, Pacific Coastal and Marine Science Center
Contact_Position: Geologist
Contact_Address:
Address_Type: Physical and Mailing
Address: 2885 Mission St.
City: Santa Cruz
State_or_Province: CA
Postal_Code: 95060
Country: USA
Contact_Voice_Telephone: 831-460-7454
Contact_Electronic_Mail_Address: aritchie@usgs.gov
Process_Step:
Process_Description:
IMAGE QA/QC -- Original and converted images were counted, and the beginning and end of the survey are reviewed to cull extraneous images (such as camera testing or inadvertently triggered images). A multi-page contact sheet of images was created to allow quick review ensuring that (a) conversion was successful with no corrupted imagery, and (b) "extra" imagery not capturing the intended view was culled. If corrupted converted images were found, imagery is re-converted until a collection of valid images remains. Note that in some cases, water-only images may be retained if there were visible or potentially visible bathymetric features, aquatic vegetation, and/or objects in the scene that may be useful for future data applications.
Process_Date: 20200912
Process_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Andrew R. Ritchie
Contact_Organization:
U.S. Geological Survey, Pacific Coastal and Marine Science Center
Contact_Position: Geologist
Contact_Address:
Address_Type: Physical and Mailing
Address: 2885 Mission St.
City: Santa Cruz
State_or_Province: CA
Postal_Code: 95060
Country: USA
Contact_Voice_Telephone: 831-460-7454
Contact_Electronic_Mail_Address: aritchie@usgs.gov
Process_Step:
Process_Description:
AIRCRAFT NAVIGATION PROCESSING -- Raw GNSS data received by the antenna mounted atop the aircraft were recorded at 1 Hz by a dual-frequency survey-grade GNSS receiver, which was post-processed and differentially corrected with no fewer than 5 continuously operating reference stations (CORS) using NovAtel's GrafNav software to produce 1-Hz aircraft trajectories.
The aircraft trajectories, in combination with precisely recorded image capture (flash event) times, are used to generate aircraft GNSS antenna positions at the moment of each image capture (NC_OBX_20200802_preIsaias_AircraftPositions.txt). The positions in the aircraft navigation file represent the position of the aircraft GNSS antenna, not the position of the camera or features photographed. To determine actual image positions, photogrammetric software such as Agisoft Metashape can be used to apply the lever arm offsets (in the camera frame of reference) from the GNSS antenna reference point to the camera lens, which are 0.1 m, -0.15 m, and 1.25 m, in the x, y, and z directions respectively, see Over and others (2021) for more details.
Process_Date: 20200924
Process_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Christine J. Kranenburg
Contact_Organization:
U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center
Contact_Position: Cartographer
Contact_Address:
Address_Type: Physical and Mailing
Address: 600 4th Street South
City: St. Petersburg
State_or_Province: FL
Postal_Code: 33701
Country: USA
Contact_Voice_Telephone: 727-502-8000
Contact_Electronic_Mail_Address: ckranenburg@usgs.gov
Process_Step:
Process_Description:
IMAGERY HEADERS -- Georeferencing, copyright, and other relevant information was added to the imagery header of each image using Phil Harvey's ExifTool. To extract the information from the image headers using ExifTool, the following command can be used (tested with ExifTool):
exiftool -n -csv *.tif > allheaders.csv
The -csv flag writes the information out in a comma-delimited format. The -n option formats the latitude and longitude as signed decimal degrees.
Process_Date: 20230902
Process_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Christine J. Kranenburg
Contact_Organization:
U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center
Contact_Position: Cartographer
Contact_Address:
Address_Type: Physical and Mailing
Address: 600 4th Street South
City: St. Petersburg
State_or_Province: FL
Postal_Code: 33701
Country: USA
Contact_Voice_Telephone: 727-502-8000
Contact_Electronic_Mail_Address: ckranenburg@usgs.gov
Process_Step:
Process_Description:
KMZ CREATION -- In order to provide a visual map of the survey extent with example images throughout the survey domain, and to aid in completing the geospatial information in the collection-level metadata, a clickable Keyhole Markup Language Zipped file (.kmz) is created for each collection using ExifTool.
Process_Date: 20230922
Process_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Christine J. Kranenburg
Contact_Organization:
U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center
Contact_Position: Cartographer
Contact_Address:
Address_Type: Physical and Mailing
Address: 600 4th Street South
City: St. Petersburg
State_or_Province: FL
Postal_Code: 33701
Country: USA
Contact_Voice_Telephone: 727-502-8000
Contact_Electronic_Mail_Address: ckranenburg@usgs.gov
