Radiometric measurements over bare and vegetated fields at 1.4-GHz and 5-GHz frequencies

Microwave radiometry of vegetation canopies

“…Different combinations of brightness temperatures measured at the same wavelength but at different polarizations (v or h) and at different obser- It should be noted that, as a matter of fact, this index is usually named as the polarization index itself (e.g., Wang et al, 1982a;Paloscia and Pampaloni, 1988;Owe et al, 2001) and, sometimes, the half-sum of the brightness temperatures is used in the denominator of the ratio. .…”

“…No attempt was made to quantify the vegetation effect. Jackson et al (1982) and Wang et al (1982a) reported about a series of experiments conducted by NASA and USDA during October, 1979 and the summer of 1980 on plots located on Beltsville Agricultural Research Center in Maryland. Plot land covers included bare soil, corn, soybeans, and orchard grass.…”

“…It was found that the C-band system alone is of little value in estimating the soil moisture under vegetation canopies because of a rather great error of soil moisture retrieval. The paper by Wang et al (1982a) presents detailed data on the emissivity and polarization factor (at 40° observation angle) of bare and vegetated soils as a function of the soil moisture. The presence of vegetation cover reduced the measured polarization factor (the polarization index).…”

“…The retrieval technique described above was used by many authors (Kirdiashev et al, 1979;Jackson et al, 1982;Mo et al, 1982;Wang et al, 1982a;Brunfeldt and Ulaby, 1986;Pampaloni and Paloscia, 1986;Van de Griend et al, 1996;Kruopis et al, 1999;Milshin et al, 1999).…”

“…The possibility to implement N-parameter retrievals from L-band microwave observations (N = 2, 3, 4…) was investigated in the paper based on experimental datasets acquired over a variety of crop fields. The datasets were collected during BARC (Wang et al, 1982a), PORTOS-91 and -93 (Wigneron et al, 1995(Wigneron et al, , 1993Calvet et al, 1995b), and EMIRAD experiments. The ω τ − model was considered in the retrieval: soil moisture and the roughness parameter s h , surface temperature, vegetation optical thickness, the single scattering albedo at both vertical and horizontal polarizations, and the C pol parameter (see equation (5.26)).…”