Calibration scientists talk about instrumentation
on the Salton Sea calibration platform.
Nov. 29, 2007 • The semi-annual meeting of the
Landsat Calibration Working Group was held November 28-29 in Palm
Springs, CA. Participants included representatives from the NASA/GSFC
Land-cover satellite Project Science Office and the USGS Landsat
Project who work jointly to maintain the geometric and radiometric
performance of the Landsat data products. The four vicarious
radiometric calibration teams from the University of Arizona, Rochester
Institute of Technology (RIT), Jet Propulsion Lab and South Dakota
State University (SDSU) attended and Ball Aerospace, the Operational
Land Imager contractor for the Landsat Data Continuity Mission sent
a representative.
Discussions of current Landsat-5 TM and Landsat-7
ETM+ performance did not indicate any major changes in radiometric
or geometric performance, other than those associated with the ETM+
April 1, 2007 switch to bumper mode. Several issues did arise that
will require attention:
The switch to bumper mode operation on Landsat-7 ETM+ this
year revealed some issues with the generation of the thermal band
calibration processing parameters; an interim processing procedure
has been implemented that corrects most of the problem and there
is a long term resolution with software and parameter updates in
the works. The current data processing strategy, where the data
are processed to level 1G shortly after acquisition, results in
the "fixes" not being applied to the distributed data for
the affected period of time. This is an issue for other geometric
and radiometric parameter updates as well and is currently being
worked by USGS/EROS.
The switch to bumper mode operation of Landsat-7 ETM+ also
degraded the geodetic accuracy: Post April 1, 2007 65% of scenes
had geodetic accuracy RMSE < 50 meters; prior to this 97% met
this criterion (since the beginning of the "quiet gyro" period
on March 14, 2005). This is a consequence of the fact that the
fixed scan-start and -stop angles provided by the scan angle monitor
are not used to control the scan mirror when operating in bumper
mode.
The current several month hiatus in the Landsat-5 TM operations
due to battery problems will result in some geometric (and perhaps
radiometric) discontinuities and intensive calibration efforts
if and when operations resume.
Work is also progressing on tying the Landsat-4 TM radiometric calibration
to Landsat-5 TM and very encouraging results were presented on verifying
the Landsat-5 TM thermal band calibration prior to Landsat-7 launch
using buoys on the Great Lakes.
The team visited Simon Hook’s (JPL) thermal vicarious calibration
platform on the Salton Sea. The site has the advantage of providing
a large water body at warm temperatures in the summer providing a higher
temperature for thermal calibration. It is a challenging environment
to work in due to the high salinity (and other dissolved materials)
of the water.