Abstract. Determination of aerosol optical properties with orbital passive remote
sensing is a difficult task, as observations often have limited information.
Multi-angle instruments, such as the Multi-angle Imaging SpectroRadiometer
(MISR) and the POlarization and Directionality of the Earth's Reflectances
(POLDER), seek to address this by making information-rich multi-angle
observations that can be used to better retrieve aerosol optical
properties. The paradigm for such instruments is that each angle view is made
from one platform, with, for example, a gimballed sensor or multiple fixed
view angle sensors. This restricts the observing geometry to a plane within
the scene bidirectional reflectance distribution function (BRDF) observed at
the top of the atmosphere (TOA). New technological developments, however,
support sensors on small satellites flying in formation, which could be a
beneficial alternative. Such sensors may have only one viewing direction
each, but the agility of small satellites allows one to control this
direction and change it over time. When such agile satellites are flown in
formation and their sensors pointed to the same location at approximately the
same time, they could sample a distributed set of geometries within the scene
BRDF. In other words, observations from multiple satellites can take a
variety of view zenith and azimuth angles and are not restricted to one
azimuth plane as is the case with a single multi-angle instrument. It is not
known, however, whether this is as potentially capable as a multi-angle platform
for the purposes of aerosol remote sensing. Using a systems engineering tool
coupled with an information content analysis technique, we investigate the
feasibility of such an approach for the remote sensing of aerosols. These
tools test the mean results of all geometries encountered in an orbit. We
find that small satellites in formation are equally capable as multi-angle
platforms for aerosol remote sensing, as long as their calibration accuracies
and measurement uncertainties are equivalent. As long as the viewing
geometries are dispersed throughout the BRDF, it appears the quantity of view
angles determines the information content of the observations, not the
specific observation geometry. Given the smoothly varying nature of BRDF's
observed at the TOA, this is reasonable and supports the viability of
aerosol remote sensing with small satellites flying in formation. The
incremental improvement in information content that we found with number of
view angles also supports the concept of a resilient mission comprised of
multiple satellites that are continuously replaced as they age or fail.
The Normalized Difference Vegetation Index and Angular Variation of Surface Spectral Polarized Reflectance Relationships: Improvements on Aerosol Remote Sensing Over Land
