Multispectral aerial imagery from unmanned aerial systems (UAS) flights and image locations: Plum Island Estuary and Parker River NWR (PIEPR), February 27th, 2018

Equipment_and_Setup: A MicaSense RedEdge multispectral camera was mounted on a 3DR Solo quadcopter. MicaSense RedEdge acquires photos at 1.2 Megapixels in 12-bit DNG format. The resolution is 1280 X 960 pixels. MicaSense RedEdge lens focal length is 5.5mm, it has global shutters for all bands, blue, green, red, red edge, and near infrared, with an aperture f2.8. File sizes are generally 1.8 MB on disc. The look direction was directly down from the aircraft. For flight, the camera was set to record images at 2-second intervals, activated before takeoff and deactivated after landing. Flights were flown along pre-planned lines and lasted the duration of the UAS battery life (approximately 15 minutes) or until the flight was completed or aborted. At the start of the mission and throughout the day, the camera shutter was manually triggered with the UAS held over a MicaSense Calibrated Reflectance Panel. The camera was not mounted on a gimbal so capture scenes were dependent on the attitude of the quadcopter.
3DR GPS module and MicaSense downwelling Light Sensor were connected to the camera with 6-pin cables and secured on top of the aircraft with velcro. The camera received power from a connection to the UAS. The 3DR GPS module is a pre-configured u-Blox NEO-7 that uses a 25 x 25 x 4 mm ceramic patch antenna with a 5 Hz update rate. It records telemetry information including latitude, longitude, altitude, dilution of precision, date and time, roll, pitch, and yaw. The downwelling light sensor measures ambient light for each of the 5 spectral bands captured by the camera. For each camera shutter trigger, it recorded spectral data including spectral irradiance, roll, pitch, yaw, gain, and exposure time. Data from the downwelling light sensor, and GPS module are automatically incorporated into the Exif data for each image.

Five images are collected at each time point. One image for each of the five wavelengths (each lens is a different wavelength Blue- 475nm, Green- 560nm, Red- 668nm, Red Edge- 717nm, Near IR- 840nm). The underscore in the image name is followed by the band number; _1 corresponds to blue, _2 corresponds to green, _3 corresponds to red, _4 corresponds to red edge, and _5 corresponds to near infrared. Before the images can be used to create photogrammetry products they need to be radiometrically calibrated to account for changing light conditions.
Before flight, calibration photos are taken of a MicaSense calibrated reflectance panel. The photos are calibrated using a photogrammetry software package (Pix4D), and the images taken of a calibrated reflectance panel, standardized reflectance values provided by Micasense, and data from the downwelling light sensor stored in the image headers. The reflectance values for the panel are 0.61 for near infrared, 0.63 for blue, and 0.64 for green, red and rededge. Calibration photos should be chosen to temporally match the UAS photos as closely as possible. Radiometric differences between files may be due to changing light conditions during flight.

After a flight, the SD card is removed from the camera, and all files related to the flight are downloaded and organized by flight number. ExifTool by Phil Harvey (version 10.99) was used to update the image names, and to update metadata in image headers.
An example script for renaming and adding Exif tags for flight 1 can be pasted into a command line (an example of this script to rename and tag flight 1 is):
exiftool-d 2018015FA_f01m01_%Y%m%dT%H%M%SZ_%%f.%%e "-filename<CreateDate" -Artist="WHCMSC AIM Group" -Credit="U.S. Geological Survey" -Contact="WHSC_data_contact@usgs.gov" -sep "; " -keywords="Plum Island; USGS; MA; 2018-015-FA; UAS; nadir; multispectral; https://doi.org/10.5066/P9O9NSRK" -Copyright="Public Domain. Please credit U.S. Geological Survey" -UserComment="F1" -Caption="Low-altitude aerial photography of Plum Island, MA from survey 2018-015-FA (https://cmgds.marine.usgs.gov/fan_info.php?fa=2018-015-FA)." -ImageDescription="Low-altitude aerial photograph of Plum Island, MA from survey 2018-015-FA (https://cmgds.marine.usgs.gov/fan_info.php?fa=2018-015-FA)." -Caption-Abstract="Low-altitude aerial photography of Plum Island, MA from survey 2018-015-FA (https://cmgds.marine.usgs.gov/fan_info.php?fa=2018-015-FA)." -CopyrightNotice="Public Domain. Please credit U.S. Geological Survey" path\to\imagedirectory
All TIFF images were renamed to ensure unique filenames and compliance with USGS Coastal/Marine Hazards and Resources Program's best practices for image naming convention. An example filename for this dataset is 2018015FA_f01m01_20180227T161137Z_IMG_0061_4, where 2018015FA is the internal survey ID, f01m01 is the flight number and internal camera ID, 20180227 is the UTC date in format YYYYMMDD, A 'T' is used to separate UTC date from UTC time in format HHMMSS (161137) followed by a Z, and IMG_0061_4 is the original raw photo name appended to the end of the new filename.
The following tags were updated with standardized values in the image headers to enhance the metadata available:
Artist-WHCMSC AIM Group
Credit- U.S. Geological Survey
Contact- WHSC_data_contact@usgs.gov
keywords- Plum Island, USGS, MA, 2018-015-FA, UAS, nadir, multispectral, https://doi.org/10.5066/P9O9NSRK
Copyright- Public Domain. Please credit U.S. Geological Survey
UserComment- F1 (the flight number)
Caption- Low-altitude aerial photograph of Plum Island, MA from survey 2018-015-FA (https://cmgds.marine.usgs.gov/fan_info.php?fa=2018-015-FA).
ImageDescription- Low-altitude aerial photograph of Plum Island, MA from survey 2018-015-FA (https://cmgds.marine.usgs.gov/fan_info.php?fa=2018-015-FA).
Caption-Abstract- Low-altitude aerial photograph of Plum Island, MA from survey 2018-015-FA (https://cmgds.marine.usgs.gov/fan_info.php?fa=2018-015-FA).
CopyrightNotice- Public Domain. Please credit U.S. Geological Survey
GPSTimeStamp- (time copied from -DateTimeOriginal)
GPSDateStamp- (date copied from -DateTimeOriginal)
The images are stamped with a date/time stamp recieved from the internal GPS. This populates the Exif tag -Date/Time Original.

The MicaSense rededge camera records GPS time and date from the GPS connected to the camera. This populates the Exif tag -Date/Time Original. In this process step ExifTool was used to copy the -Date/Time Original stamp into the Exif tag -GPSTimeStamp, and GPSDateStamp.
This step was done as a batch script, with text-
for f in f*/*.tif; do exiftool "-GPSTimeStamp<CreateDate" "-GPSDateStamp<CreateDate" $f -overwrite_original; done
Where $f was the previously edited images.
Calibration images were omitted from this process.

ExifTools version 11.28 was used to extract a subset of the Exif header information from the multispectral aerial images to provide image location information in a separate file. The command to extract the information is as follows:
exiftool.exe -csv -filename -GPSDateStamp -GPSTimeStamp -GPSLongitude -GPSLatitude -GPSAltitude -n fX\*.tif > UASmica_nav_fX.csv
where fX is the folder name which is the same as the flight number in the format fX where X is the flight number.
This command was run from a DOS command window on a Windows 7 machine.
Once a separate file was extracted for each flight, the individual files were concatenated together (UASmica_2018015FA_nav.csv) using the cat command in Cygwin. The VI editor was then used to remove all but the first occurrence of the header line.
Calibration images were omitted from this process.

Added keywords section with USGS persistent identifier as theme keyword.