Location: Hydrology and Remote Sensing LaboratoryTitle: Monitoring soybean growth using L, C, X-band scatterometer data) Author
Submitted to: International Journal of Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2013
Publication Date: 12/20/2013
Publication URL: http://handle.nal.usda.gov/10113/56301
Citation: Kim, Y., Jackson, T.J., Bindlish, R., Lee, H., Hong, S. 2013. Monitoring soybean growth using L, C, X-band scatterometer data. International Journal of Remote Sensing. 11:4069-4082. Interpretive Summary: A ground-based fully polarimetric scatterometer operating at multiple frequencies (L-, C- and X-band) was used to continuously monitor the crop conditions of soybean. Remote sensing is an effective tool in monitoring soybean growth and yield assessment. Conventional visible and near infrared remote sensing techniques are widely used; however, they have limitations. Microwave remote sensing offers some potential improvements over conventional remote sensing due to its all-weather day-and-night imaging capabilities and because radar waves penetrate into the vegetation canopies. Ground-based polarimetric scatterometer systems are very valuable in establishing basic relationships because target and system parameters can be well controlled. The results of this investigation showed that L-band radar observations can be used to accurately retrieve vegetation growth parameters. The experiment design and results are particularly relevant to the NASA Soil Moisture Active Passive (SMAP) satellite scheduled for 2014, which will provide important soil moisture and vegetation information for agricultural decision making.
Technical Abstract: A ground-based fully-polarimetric scatterometer operating at multiple frequencies was used to continuously monitor soybean growth over the course of a growing season. Polarimetric backscatter data at L-, C- and X-bands were acquired every 10 minutes. We analyzed the relationships between L-, C- and X-band signatures, biophysical measurements, and volumetric soil moisture (VSM) over the entire soybean growth period. Temporal changes in backscattering coefficients for all bands followed the patterns observed in the soybean growth measurements (Leaf Area Index (LAI) and Vegetation Water Content (VWC). The difference between the backscattering coefficients for HH and VV-polarizations at L-band was significant after the R2 stage (DOY 224) due to the double bounce scattering effect. L, C, and X-band radar backscatter data can be used to detect different soybean growth stages. The results of correlation analyses between the backscattering coefficient for specific bands/polarizations and soybean growth data showed that L-band HH-polarization was the best suited for monitoring LAI (r=0.98), VWC (r=0.97) and VSM (r=0.90). It was observed that the observed backscatter coefficient increases as the soil moisture increases. Prediction equations for estimation of soybean growth parameters from the L-HH were developed. The results indicated that L-HH could be used for estimating the vegetation biophysical parameters considered here with high accuracy. These results provide a basis for developing a method to retrieve crop biophysical properties and guidance on the optimum microwave frequency and polarization necessary to monitor crop conditions. The results are directly applicable to systems such as the proposed NASA Soil Moisture Active Passive (SMAP) satellite.