Remote Sensing of Cloud Properties Using Ground-Based Measurements of Zenith Radiance

Journal Article · Fri Aug 18 04:00:00 EDT 2006 · Journal of Geophysical Research. D. (Atmospheres), 111(D16):D16201

DOI:https://doi.org/10.1029/2005JD006843· OSTI ID:891427

Chiu, J.-Y. C.; Marshak, A; Knyazikhin, Y; Wiscombe, Warren J; Barker, H W; Barnard, James C; Luo, Yi

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 nm wavelengths and require the presence of green vegetation in the surrounding area. The test was conducted at the ARM Oklahoma site during September to November 2004. These methods work because, at 673 nm (RED) and 870 nm (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. Due to the one-second time resolution of our radiance measurements, we are able, for the first time, to capture changes in cloud optical properties at the natural time scale 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 retrieval, this is not always the case. In general, however, the COUPLED and REDvsNIR methods retrieve--to within 15% of each other.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 891427
• Report Number(s): PNNL-SA-49174
• Journal Information: Journal of Geophysical Research. D. (Atmospheres), 111(D16):D16201, Journal Name: Journal of Geophysical Research. D. (Atmospheres), 111(D16):D16201
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
CLOUDS
FIELD TESTS
MEASURING METHODS
OKLAHOMA
OPTICAL PROPERTIES
REMOTE SENSING
cloud fraction
cloud optical depth
retrieval algorithm