R. Kahn et al., Sensitivity of multiangle imaging to aerosol optical depth and to pure-particle size distribution and composition over ocean, J GEO RES-A, 103(D24), 1998, pp. 32195-32213
Multiangle, multispectral remote sensing observations, such as those antici
pated from the Earth Observing System (EOS) Multiangle Imaging Spectroradio
meter (MISR), can significantly improve our ability to constrain aerosol pr
operties from space. Simulations over cloud-free, calm ocean conditions wer
e studied for pure particles with natural ranges of optical depth, particle
size, and indices of refraction. According to the theoretical simulations
we can retrieve column optical depth from measurements over calm ocean for
all but the darkest particles, with typical size distributions and composit
ions, to an uncertainty of at most 0.05 or 20%, whichever is larger, even i
f the particle properties are poorly known. For one common particle type, s
oot, constraints on the optical depth over dark ocean are very poor. The si
mulated measurements also allow us to distinguish spherical from nonspheric
al particles, to separate two to four compositional groups based on indices
of refraction, and to identify three to four distinct size groups between
0.1 and 2.0 mu m characteristic radius at most latitudes. The technique is
most sensitive to particle microphysical properties in the "accumulation mo
de" sizes, where particle scattering undergoes the transition from Rayleigh
to large-particle regimes for the MISR wavelengths. On the basis of these
results we expect to distinguish air masses containing different aerosol ty
pes, routinely and globally, with multiangle remote sensing data. Such data
complement in situ and field data, which can provide detailed information
about aerosol size and composition locally. An extension of this study to m
ixtures of pure particles is part of continuing work.