Contact Us

251 Fuller Rd
Albany, NY 12203

Ground-based remote sensing of cloud optical properties

The reflectivity of cirrus cloud measured by the MMCR, and inferred optical depths of aerosol and cloud at the ARM SGP site on March 13, 2000. (Min et al 2004)

Joint statistics of mean and variance of photon path length with cloud optical depth in O2 and H20 bands.
(Min and Clothiaux, 2003)


Clouds remain the greatest sources of uncertainty in global climate change research. The impact of greenhouse warming on cloud amount through climate feedback can make significant changes in the global radiative energy balance. Knowledge of cloud properties and their spatial and temporal variation is crucial to advance understanding of global climate change.

We developed a family of ground based remote sensing algorithms for inferring aerosol and cloud optical properties using Multifilter Rotating Shadowband Radiometer (MFRSR) measurements, including

Aerosol retrievals:

    Aerosol optical depth

    Angstrom coefficients [Min et al, 2004a]

    Single scattering albedo (SSA)

Cloud retrievals:

    Optical depth (5 and up) and effective radius from diffuse [Min and Harrison, 1996];[ Min et al, 2003]

    Optical depths of aerosols and thin clouds (0 ~ 7) from direct beam [Min et al, 2004a]; [[Min et al, 2004b]

    Cloud phase [Wang and Min 2008]

    Cloud fraction [Min et al. 2008]

Synthesis radiation spectra of UVB and PAR [Min and Harrison, 1998]; [Min 2005]

Photon path length distribution and oxygen A-band spectral measurements:

For a long time the remote sensing community has recognized the advantages of retrieval using the oxygen A-band, and has sought ways to exploit these advantages to measure atmospheric properties and constituents. Because oxygen is a well-mixed gas in the atmosphere, the pressure dependence (as a surrogate of altitude) of oxygen A-band absorption line parameters provides a vehicle for retrieving photon path length distributions from spectrometry of the oxygen A-band. The concept underling oxygen A-band retrievals is the principle of equivalence, which allows assessment of atmospheric radiative properties at any nearby wavelength from a photon path length distribution measurement at one particular band. This is possible because the scattering properties of cloud and aerosol vary slowly and predictably with wavelength and 760 nm is a useful central wavelength, reasonably representative of the entire solar shortwave. Photon path length distributions, a hidden property of standard radiation transfer models and controlled by spatial distributions of scattering and absorption, can be retrieved through an inverse Laplace transform based on the equivalence theorem.

[Harrsion and Min 1997] ;

[Min and Harrison, 1999];

[Min et al. 2001];

[Min and Clothiaux 2003];

[Min et al. 2004];

[Min and Harrison. 2004]

Retrievals of aerosol and cloud optical properties from the forward scattering lobe:

We proposed a new technique for simultaneously retrieving cloud optical depth and effective radius for low LWP clouds by modifying current existing MFRSRs [Min and Duan 2005]. This approach is based on the angular distribution of scattered light in the forward scattering lobe of aerosol and cloud particles. More to see [Instrument Development]