The Remote Sensing Group at the University of Arizona has developed an automated methodology and instrument suite
to measure the surface reflectance of the vicarious calibration test site at Railroad Valley, Nevada. Surface reflectance is
a critical variable used as one of the inputs into a radiative transfer code to predict the top-of-atmosphere radiance, and
inexpensive and robust ground-viewing radiometers have been present at the site since 2004. The goal of the automated
approach is to retain RSG's current 2-3% level of uncertainty while increasing the number of data sets collected
throughout the year without the need for on-site personnel. A previous study was completed to determine if the number
and positions of the four radiometers were adequate to spatially sample the 1-km2 large-footprint site at Railroad Valley.
The preliminary study utilized one set of panchromatic data from Digital Globe's QuickBird satellite. Results from this
one day showed that the positions of the four ground-viewing radiometers adequately sample the site.
The work presented here expands in a spectral and temporal sense by using high-spatial-resolution data from Ikonos,
QuickBird, and Landsat-7 ETM+ to determine if the locations of the ground-viewing radiometers correctly sample the
site. The multispectral capability of these sensors is used to establish if there are any spectral effects, which will also
help RSG to determine what spectral bands should be chosen for the new ground-viewing radiometers that are currently
in development for the automated test site at Railroad Valley.
The recent deployment of on-orbit active sensors operating at optical wavelengths requires new calibration methods to
be investigated. In response to this, a ground-based active radiometer for measuring backscattered surface reflectance
has been developed by the Remote Sensing Group at the University of Arizona. This instrument, known as the
reflectometer, was designed to match the illumination and detection geometry of spaceborne lidar systems. The
reflectometer uses a Nd:YAG laser operating at 1064 nm (with the capability of 532 nm), illuminates the target sample
at normal incidence by use of a beam expander and fold mirror, then collects the reflected light at nadir through an
aperture in the fold mirror. In order to reduce stray light, a 3 nm bandwidth filter centered on the laser wavelength is
mounted in front of the silicon detector and a half cylinder shell encloses the optical system. Previous measurements at
White Sands Missile Range, NM have produced results that are within 3% of coincident measurements using a field
spectrometer.1 The results of these measurements are presented, including further laboratory testing using tarpaulin
witness samples and future improvements of the original system design. In addition, comparison of reflectometer
measurements to MODIS derived reflectance as it relates to on-orbit lidar retroreflection will be discussed. The benefits
of validating MODIS derived reflectance will become essential with the launch of CALIPSO and its incorporation into
the A-train.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.