UDI: MS.x839.000:0029

Dataset Abstract:

This data comprises imagery collected from an unmanned aerial system (DJI M600 Matrice) 
over oyster reefs in the Bay of St. Louis near Gulfport, MS.  

This dataset was collected with the goal of observing water quality from a remote 
platform.  In particular, the hyperspectral data collected to observe relevant 
phenomena, and is meant to be evaluated along with the MicaSense RedEdge data 
collected simultaneously, although that data is not required to achieve all mission goals.

This dataset is associated with MS.x839.000:0025 (processed multispectral).

Purpose:

Collection of Headwall Nano-Hyperspec hyperspectral imagery to correlate with 
simultaneously-collected MicaSense RedEdge imagery. The goal is to determine 
whether the relevant water quality phenomena can be detected using a cheaper 
5-band sensor.

Supplemental Information: Data Parameters and Units
Imagery was collected using a Headwall Nano-Hyperspec sensor, a pushbroom 
hyperspectral sensor that produces a line of pixel data 640 pixels wide.  
These are stored in chunks of data that can contain a user-specified number
of lines per hyperspectral image file. The spectral range of the imager is 
from 400-1000 nm in wavelength, although the lower and upper 50 nm tend to 
be less accurate.  The spectral resolution is approximately 2-3 nm per band, 
and the sensor records 270 of these bands in total.

The horizontal field-of-view of this sensor is 52 degrees (4.8 mm lens).

Sensor orientation is recorded by a separate GPS/inertial measurement unit (IMU) 
mounted to the sensor.  The orientation is recorded in the "imu_gps.txt" file.  
Note that there are two sensors that have been used; post-July, a newer sensor 
with a wider-angle lens and more accurate GPS/IMU was used.

Data values are stored as 32-bit floating point numbers, representing reflectance, 
a unitless measurement that codifies the percentage of light reflected from a surface 
within the given light wavelength.  These should range from 0.0 to 1.0, although 
values less than or greater may be encountered in saturated pixels or those within 
the range of the imager noise threshold, depending on when the calibration tarp 
image was taken and if lighting conditions have changed in the time between line captures.

Images are stored in ENVI image format, which takes the form of a binary file and image 
description pair.  In some cases, the processed data will be in a single file, 
for example, "multi_or_rf/multi_or_rf.hdr", with the "or" and "rf" extensions 
denoting that the imagery has been both orthorectified and reflectance-corrected. 
In other cases, the image set will be broken into chunks based on flight lines, 
which both helps process the data more efficiently and avoids mixing overlapping 
data on each flight line, producing more usable data.

Data was calibrated to 11% reflectance target. This allows observation of water 
quality (less than 10% reflectance) without saturation, while saturating on unimportant areas.

Headwall's processing software converts the raw DNs into reflectance and 
orthorectifies the data.

The orthomosaic process places the data close to where it should reside on a 
map, but due to inaccuracies in both the GPS and IMU, this will not be perfect. 
The lack of visible tie points makes this impossible to post-correct.

Lighting condition changes during flight will affect the accuracy of reflectance 
values. If there is cloud cover, the data collected during that period will not 
be accurate.