Validation Field Instruments |
| CIMEL |
The CIMEL sun/sky photometer system is capable of long-term independent operation
for measurements of direct solar irradiance and sky radiances used to determine
optical depth and aerosol scattering and absorption properties. The sensor
head is attached to a fully automated mechanism that carries out direct beam
solar measurements as well as sky radiance measurements in the solar almucantar
and in the solar principal plane. Two collimators feed detectors for measurement
of direct sun, aureole and sky radiance. There are 8 interference filters
at various wavelengths and 3 polarizing filters at 870 nm. |
| Link to CIMEL data |
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| Reagan Sunphotometer |
This battery powered automated-tracking solar radiometer was developed at
the University of Arizona. It contains 10 sensors at wavelengths from 380
nm to 1028 nm with bandwidths of 7 to 17 nm. It is used to gather data that
will determine atmospheric aerosol optical depth, estimate ozone optical
depth and the column abundance of atmospheric precipitable water. Tracking
accuracy is ± 0.05° and the system maintains solar tracking in
the presence of occasional small clouds. Data collection is possible for
up to an entire day at intervals adjustable from 10 seconds to several minutes.
The MISR Validation Team has two essentially identical instruments, giving
them the opportunity of comparing results. |
| Link to Reagan Sunphotometer data |
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| ASD |
The Analytical Spectral Devices Field Spectrometer (here abbreviated ASD)
is a portable, light weight, battery powered instrument that uses a fiber-optic
cable to sample the light field being measured. Inside the instrument the
fiber-optic bundle within the cable is divided into three bundles. Each bundle
delivers the collected light to the entrance slit of one of three spectrometers
covering the spectral range 350-2500 nm. The first spectrometer covers the
wavelength region from 350-1000 nm with a sampling interval of 1.4 nm and
a spectral resolution of approximately 3 nm. The second spectrometer covers
the interval 900 nm to 1800 nm and the third from 1700 nm to 2500 nm. The
spectral sampling interval of the second and third spectrometers is 2 nm
and spectral resolution is 10-11 nm. The fiber optic cable has a full view
angle of 25°, with special attachments allowing restriction to 8°.
The total spectral acquisiton time is on the order of a few seconds per spectrum
depending on integration time chosen, making the instrument very useful for
rapid acquisition of large numbers of ground spectra which can be used to
form average reflectances of large natural target areas. |
| Link to ASD data |
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| MFRSR |
The Multi-Filter Rotating Shadowband Radiometer (MFRSR) is a portable instrument
that determines nearly simultaneous global and diffuse components of the
solar spectral irradiance. From these an estimate of the imaginary part of
the aerosol refractive index and an average surface Lambertian reflectance
can be found. It uses independent interference filter-photodiode combinations
that are mounted in a temperature-controlled enclosure for measurement of
spectral irradiance at six wavelengths and one broadband channel. A rotating
shadowband moves to four positions, blocking the instrument entrance aperture
occulting the direct solar beam plus adjacent aureole components, observations
on either side to correct for excess blocked sky during the sun occultation,
and a rest position. |
| Link to MFRSR data |
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| PARABOLA |
The Portable Apparatus for Rapid Acquisition of Bidirectional Observation
of the Land and Atmosphere (PARABOLA) is a sphere-scanning 8 channel radiometer
system that generates radiance measurements from a transportable platform
mount over both ground and sky. Observations will be utilized to calculate
bidirectional reflectance factors of the surface, and by spatial integration,
the hemispherical directional and bihemispherical reflectances (HDR and BHR,
respectively), plus the downwelling total and diffuse irradiances at the
surface. During its 3 minute cycle it takes measurements at 72 azimuthal
and 37 elevation positions. |
| Link to PARABOLA data |
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| AirMISR |
The Airborne Multi-angle Imagery SpectroRadiometer (AirMISR) is an
important tool in the MISR validation program. Whereas our other field
instrument can only take samples of data at one location at a time, AirMISR
can fly over a region, and better allow us to gather enough information to
compare to the MISR observations. This is particulary important because
MISR samples Earth in no smaller than 250 meter chunks at a time. This
area is large compared to the fraction of a meter seen by the other
validation field instrument. AirMISR is thus an important bridge between
the extremes of the field instruments, and MISR. |
| Link to AirMISR Page |
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