L Band Observations Over A Corn Canopy During the Entire Growing Season

Authors: JOSEPH, A - NASA GSFC; VAN DER VELDE, R - INT. INST. FOR GEO-INFO.; O'NEILL, P - NASA GSFC; CHOUDHURY, B - NASA GSFC; LIANG, S - UNIV. OF MD; LANG, R - GEORGE WASHINGTON UNIV.; KIM, E - NASA GSFC; Gish, Timothy; HOUSER, P - GEORGE MASON UNIV.

Submitted to: International Journal of Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2007
Publication Date: 6/1/2008
Citation: Joseph, A.T., Van Der Velde, R., O'Neill, P.E., Choudhury, B.J., Liang, S., Lang, R.H., Kim, E., Gish, T.J., Houser, P.R. 2008. L Ban observations over a corn canopy during the entire growing season. International Journal of Remote Sensing. 46(8):1-11.

Interpretive Summary: New opportunities for large-scale soil moisture monitoring will emerge with the launch of two low frequency (L-band 1.4 GHz) radiometers: the European Space Agency’s Soil Moisture and Ocean Salinity (SMOS) and the NASA Aquarius missions. In anticipation of data to be acquired by these missions an experiment was conducted to analyze microwave responses from crop emergence to senescence. An extensive set of land surface variables were also obtained that included soil moisture, soil temperature, vegetation biomass, and surface roughness. The focus of this analysis was to investigate the effect of vegetation on microwave observations throughout a complete corn growth cycle. The results show that for sparse vegetation the transmissivity of the canopy layer was lower than expected while for dense vegetation the transmissivity was found to be higher than expected. This data will be used to improve algorithms for hydrologic modeling as well as climate and crop growth models.

Technical Abstract: New opportunities for large-scale soil moisture monitoring will emerge with the launch of two low frequency (L-band 1.4 GHz) radiometers: the European Space Agency’s Soil Moisture and Ocean Salinity (SMOS) and the NASA Aquarius missions. In anticipation of data to be acquired by these missions an experiment was conducted to analyze microwave responses from crop emergence to crop senescence. During this field campaign, a new dual polarized L-band radiometer provided microwave observations designed to provide measurements throughout a day at preset intervals at preset incidence and azimuth angles. An extensive set of land surface variables were obtained that included soil moisture, soil temperature, vegetation biomass, and surface roughness. The focus of this analysis is to investigate the effects of vegetation on observed horizontally polarized brightness temperatures throughout a corn growth cycle. The results show that for sparse vegetation the transmissivity of the canopy layer was lower than expected based on a comparison with values in the literature, while for dense vegetation the transmissivity was found to be higher than expected. The first observation can be attributed to uncertainties in the brightness temperature (TB), while the latter is primarily caused by taking the single scattering albedo equal to zero in the initial transmissivity computations.