| Title | Remote sensing of cloud properties using ground-based measurements of zenith radiance |
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| Author | Chiu, J C; Marshak, A; Knyazikhin, Y; Wiscombe, W J; Barker, H W; Barnard, J C; Luo, Y |
| Source | Journal of Geophysical Research, Atmospheres vol. 111, no. 16, D16201, 2006., https://doi.org/10.1029/2005JD006843  Open Access |
| Year | 2006 |
| Alt Series | Natural Resources Canada, Contribution Series 20181086 |
| Publisher | Wiley-Blackwell |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Subjects | geophysics; remote sensing |
| Program | Canada Centre for Remote Sensing Divsion |
| Released | 2006 01 01 |
| Abstract | We have conducted the first extensive field test of two new methods to retrieve optical properties for overhead clouds that range from patchy to overcast. The methods use measurements of zenith radiance
at 673 and 870 mn wavelengths and require the presence of green vegetation in the surrounding area. The test was conducted at the Atmospheric Radiation Measurement Program Oklahoma site during September-November 2004. These methods work because at
673 nm (red) and 870 nm (near infrared (NIR)), clouds have nearly identical optical properties, while vegetated surfaces reflect quite differently. The first method, dubbed REDvsNIR, retrieves not only cloud optical depth ? but also radiative cloud
fraction. Because of the 1-s time resolution of our radiance measurements, we are able for the fast time to capture changes in cloud optical properties at the natural timescale of cloud evolution. We compared values of ? retrieved by REDvsNIR to
those retrieved from downward shortwave fluxes and from microwave brightness temperatures. The flux method generally underestimates ? relative to the REDvsNIR method. Even for overcast but inhomogeneous clouds, differences between REDvsNIR and the
flux method can be as large as 50%. In addition, REDvsNIR agreed to better than 15% with the microwave method for both overcast and broken clouds. The second method, dubbed COUPLED, retrieves ? by combining zenith radiances with fluxes, While extra
information from fluxes was expected to improve retrievals, this is not always the case. In general, however, the COUPLED and REDvsNIR methods retrieve ? to within 15% of each other. |
| GEOSCAN ID | 311440 |
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