Sensitivity of Passive Microwave Observations to Soil Moisture and Vegetation Water Content: L-Band to W-Band

International audience—Ground-based multifrequency (L-band to W-band, 1.41–90 GHz) and multiangular (20 • –50 •) bipolarized (V and H) microwave radiometer observations, acquired over a dense wheat field, are analyzed in order to assess the sensitivity of brightness temperatures (T b) to land surface properties: surface soil moisture (m v) and vegetation water content (VWC). For each frequency, a combination of microwave T b observed at either two contrasting incidence angles or two polarizations is used to retrieve m v and VWC, through regressed empirical logarithmic equations. The retrieval performance of the regression is used as an indicator of the sensitivity of the microwave signal to either m v or VWC. In general, L-band measurements are shown to be sensitive to both m v and VWC, with lowest root mean square errors (0.04 m 3 · m −3 and 0.52 kg · m −2 , respectively) obtained at H polarization, 20 • and 50 • incidence angles. In spite of the dense vegetation, it is shown that m v influences the microwave observations from L-band to K-band (23.8 GHz). The highest sensitivity to soil moisture is observed at L-band in all configurations , while observations at higher frequencies, from C-band (5.05 GHz) to K-band, are only moderately influenced by m v at low incidence angles (e.g., 20 •). These frequencies are also shown to be very sensitive to VWC in all the configurations tested. The highest frequencies (Q-and W-bands) are shown to be moderately sensitive to VWC only. These results are used to analyze the response of W-band emissivities derived from the Advanced Microwave Sounding Unit instruments over northern France