Skip to main content
ARS Home » Research » Publications at this Location » Publication #257635
Title: L band brightness temperature observations over a corn canopy during the entire growth cycle

Author
item JOSEPH, A - National Aeronautics And Space Administration (NASA)
item VAN DER VELDE, R - Collaborator
item O'NEILL, P - National Aeronautics And Space Administration (NASA)
item CHOUDHURY, B - National Aeronautics And Space Administration (NASA)
item KIM, E - National Aeronautics And Space Administration (NASA)
item Gish, Timothy

Submitted to: Sensors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2010
Publication Date: 9/1/2010
Citation: Joseph, A.T., Van Der Velde, R., O'Neill, P.E., Choudhury, B.J., Kim, E., Gish, T.J. 2010. L band brightness temperature observations over a corn canopy during the entire growth cycle. Sensors. 10:6980-7001.

Interpretive Summary: Low frequency passive microwave observations have been intensively studied for their potential in retrieving soil moisture estimates from agricultural fields. Although studies are typically conducted for static biomass densities configurations, they reveal that when appropriately characterized soil moisture can be retrieved fairly accurately from the brightness temperatures measured using microwave radiometers. A study was conducted at the OPE3 field site in Beltsville, Maryland to evaluate the variations in model parameters needed to describe passive and active microwave signal attenuations by corn plants during their entire growth and reproductive cycles. This study shows that the strength of scattering and absorption within a corn canopy changes throughout the growth cycle, which can be largely attributed to changes in architecture of the vegetation layer. As a result, further improvement of the soil moisture retrieval algorithm will depend largely on our ability to quantify the crop canopy architecture.

Technical Abstract: During a field campaign covering the 2002 corn growing season, a dual polarized tower mounted L-band (1.4 GHz) radiometer (LRAD) provided brightness temperature (T¬B) measurements at preset intervals, incidence and azimuth angles. These radiometer measurements were supported by an extensive characterization of land surface variables including soil moisture, soil temperature, vegetation biomass, and surface roughness. In the period May 22 to August 30, ten days of radiometer and ground measurements are available for a corn canopy with a vegetation water content (W) range of 0.0 to 4.3 kg m-2. Using this data set, the effects of corn vegetation on surface emissions are investigated by means of a semi-empirical radiative transfer model. Additionally, the impact of roughness on the surface emission is quantified using T¬B measurements over bare soil conditions. Subsequently, the estimated roughness parameters, ground measurements and horizontally (H)-polarized TB are employed to invert the H-polarized transmissivity ('h) for the monitored corn growing season.