Characterizing the dependence of vegetation model parameters on crop structure, incidence angle, and polarization at L-band

To retrieve soil moisture over vegetation-covered areas from microwave radiometry, it is necessary to account for vegetation effects. At L-band, many retrieval approaches are based on a simple model that relies on two vegetation parameters: the optical depth (/spl tau/) and the single-scattering albedo (/spl omega/). When the retrievals are based on multiconfiguration measurements, it is necessary to take into account the dependence of /spl tau/ and /spl omega/ on the system configuration, in terms of incidence angle and polarization. In this paper, this dependence was investigated for several crop types (corn, soybean, wheat, grass, and alfalfa) based on L-band experimental datasets. The results should be useful for developing more accurate forward modeling and retrieval methods over mixed pixels including a variety of vegetation types.     

Movement of Cryptolestes ferrugineus (Coleoptera: Cucujidae) in grain columns containing pockets of high moisture content wheat and carbon dioxide gradients

The movement of the adult rusty grain beetle, Cryptolestes ferrugineus (Stephens), in 100 cm long, 10 cm diameter columns, filled with wheat of uniform or non-uniform moisture content (m.c.), was determined for horizontal and vertical placement of columns at 30°C.In horizontal columns filled with wheat of 13.5% uniform m.c., adult C. ferrugineus exhibited a trend of distributing themselves uniformly in the columns after 5 d. In the vertical columns filled with 14.7% uniform m.c. wheat, 44% of the insects moved downward after 7 d showing positive geotaxism. In the horizontal or vertical columns containing pockets of high m.c. wheat, 43-48% of the beetles aggregated in the region of high m.c. after 7 d exhibiting a hygrotactic response. Under CO₂ gradients in the columns filled with uniform m.c. wheat, 65% of C. ferrugineus moved towards higher levels of CO₂ after 1 and 5 d. Also, high levels of CO₂ were more influential in attracting C. ferrugineus (60%) after 1 d in horizontal columns containing high m.c. wheat at one end and high CO₂ levels at the other. In the vertical columns filled with pockets of high m.c. wheat and subjected to CO₂ gradients, movement of C. ferrugineus was more influenced by the combined effects of any two factors out of the three, viz., gravity, higher levels of CO₂ and high m.c. than a single factor.     

N-parameter retrievals from L-band microwave observations acquired over a variety of crop fields

A number of studies have shown the feasibility of estimating surface soil moisture from L-band passive microwave measurements. Such measurements should be acquired in the near future by the Soil Moisture and Ocean Salinity (SMOS) mission. The SMOS measurements will be done at many incidence angles and two polarizations. This multiconfiguration capability could be very useful in soil moisture retrieval studies for decoupling between the effects of soil moisture and of the various surface parameters that also influence the surface emission (surface temperature, vegetation attenuation, soil roughness, etc.). The possibility to implement N-parameter (N-P) retrieval methods (where N = 2, 3, 4, ..., corresponds to the number of parameters that are retrieved) was investigated in this study based on experimental datasets acquired over a variety of crop fields. A large number of configurations of the N-P retrievals were studied, using several initializations of the model input parameters that were considered to be fixed or free. The best general configuration using no ancillary information (same configuration for all datasets) provided an rms error of about 0.059 m/sup 3//m/sup 3/ in the soil moisture retrievals. If a priori information was available on soil roughness and at least one vegetation model parameter, the rms error decreased to 0.049 m/sup 3//m/sup 3/. Using specific retrieval configurations for each dataset, the rms error was generally lower than 0.04 m/sup 3//m/sup 3/.