Detailed Description of ADF Processing
Upon receipt of an AVIRIS disk, the ADF processes the science runs
to determine whether or not the instrument performed properly over the course of the flight. This performance evaluation stage is
mainly a subset of normal processing, but is performed on the science runs on disk before normal processing can commence.
The first step in processing a new
tape is scanning the tape to make sure it matches the hardcopy list
of runs provided by the AVIRIS Experiment Coordinator.
AVIRIS processing is done on a per
run
basis.
Normal processing begins with downloading
and decommutating the data, known as the download process.
All data is stored in 16-bit integers,
The image data is reversed
(within each scan line), since the data coming off AVIRIS, if displayed
directly, is actually reversed from how the data would look from the aircraft.
Each line of data is expanded and reversed, with any bad data marked as
such, and then written to ADF archive media (external firewire hard drives).
The AVIRIS archiving process also
compiles information about the image, navigation, and engineering data
and stores it in the ADF database. This stored data is extracted at will
with the Performance Evaulation Programs, or PEPs, which also plot the
data to model instrument behavior graphically.
The AVIRIS quicklook images
are also created during the archive process. These are initially stored
grayscale JPEGs, and show band a single band of each flight run. Quicklooks can be viewed
here.
When an investigator wishes AVIRIS
data, the data must go through the
Product Generation (PG) software.
If the investigator wishes
raw data, then PG only copies the data
from archive tape to the desired distribution medium. However, most of
the time the investigator wishes radiometrically corrected data.
Radiometrically corrected means converted
into units of radiance, as opposed to the unitless AVIRIS digital numbers.
Radiance is measured in units of microwatts per square centimeter per nanometer
per steradian, or uW / (cm^2 * nm * sr). AVIRIS radiometric calibration
factors are calculated by measuring the response of AVIRIS to an integrating
sphere (a known target illuminated by a known light source). This calibration
is accurate to within 7%, absolute, over time. Intra-flight accuracy is
within 2%.
The ADF also has software for general
image processing which is used for image display and creation of pictures
for the
JPL Public Information
Office (such as this image cube) and any technical
conferences or presentations that ADF members are involved in. This software
is also used by the PEPs and for detailed anomaly analysis.
The ADF Data Subsystem:
-
- Data Processing Server: Windows 2003 Server, 17TB Disk Space
-
- FTP Server : Linux Server
-
- DVD Burning Workstation: Primera's Bravo II with ink jet label printer. DVD-R 8x Write Speed, CD-R 12x Write Speed
- 1 - Powermac G5 Workstation
- Several media devices and
peripherals
-
The ADF proprietary software are as
follows:
-
- IDL (Interactive
Display Language) from Research Systems Inc. (RSI)
-
- ENVI (ENvironment
for the Visualization of Images), also from RSI
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