Microwave emissivity of land surfaces: experiments and models

Transcription

1 Microwave emissivity of land surfaces: experiments and models M. Brogioni, G.Macelloni, S.Paloscia, P.Pampaloni, S.Pettinato, E.Santi IFAC-CNR Florence, Italy

2 Introduction Experimental investigations conducted by the Microwave Remote Sensing Group made it possible to realize a wide archive of microwave emissivity of the following surface types: bare soil with different levels of moisture and types of surface roughness soil covered with wheat, corn, alfalfa, sunflower, natural grass at various level of biomass deciduous and coniferous forests with different woody volumes soil covered with snow in different conditions (dry and wet) and depth. Ice sheet in Antarctica

3 Experimental equipments Dome-C Antarctica

4 Ground measurements

5 Experimental results: sensitivity to land features

6 TnH 1 0,95 0,9 0,85 0,8 0,75 0,7 0,65 0,6 0,55 0,5 Emissivity spectra of land surfaces FREQUENCY WHEAT CORN ALFALFA SUNFL BS (wet) BS (dry) SNOW (wet) SNOW (dry) FOREST Emissivity spectra of forests (poplar)

7 Emissivity of agricultural surfaces TnH Ka band X band L-band Soil moisture Smooth bare SMCg (%) X band L-band TnH Km Rough slightly vegetated SMCg (%)

8 Sensitivity to Plant Water Content of crops emissivity Broad leaf L X Ka Small leaf

9 NDVI from SPOT4 Sensitivity to vegetation (AMSR-E) NDVI from AMSR-E

10 Sensitivity to snow cover: dry snow accumulation Brightness Temperature (K) Snow Depth (cm) TbV meas 10GHz TbV DMRT 10GHz 170 TbV meas 37GHz TbV DMRT 37GHz Snow Water Equivalent (mm)

11 Sensitivity to snow wetness TB (37 GHz) V H T b [K] Melt-refreezing cycles W % Liquid water content

12 Sensitivity to snow cover (AMSR-E) FI Snow Depth (cm) 12/2006

13 Antarctica: Temporal variability L-band Ground based 2 week Time stability Mean = K Dev. st. = 0.18 K

14 Antarctica: Spatial variability AMSR-E (Tb 37 GHz V - Yearly average)

15 220 Antarctica: Temporal variability AMSR-E AMSR-E Brightness Temperature [K] C X Ku Ka Tsnow Retrieved [ C] cm 160 Jan-05 Apr-05 Jul-05 Oct-05 Jan-06 Apr-06 Jul-06 Oct-06 Jan-07 Date Tsnow Measured [ C] Snow Temperature [ C] Snow temp. -80 Jan-05 Apr-05 Jul-05 Oct-05 Jan-06 Apr-06 Jul-06 Oct-06 Jan-07 Date Tsnow Retrieved [ C] cm Tsnow Measured [ C]

16 Electromagnetc modelling Surface scattering: soil Volume scattering: snow vegetation crops forests

17 Sensitivity to forest biomass Emissivity Forest - Radiative Transfer ( L-Band) Trunk Total Crown Soil Incidence Angle (degs) e v eh ev eh Emissivity Data Disc. Model Cont. Model Woody Volume (m 3 /ha)

18 Model sensitivity to soil roughness V H V H ε = 7 j2 θ = 55 ε = 20 j 5 θ = 55

19 Model sensitivity to snow parameters Snow depth Grain size Snow density

20 Conclusions Microwave emissivity of land surfaces in the frequency range 1-40 GHz strongly depends on Frequency, polarization and incidence agle of the observing sensor Cover type and physical conditions Bare soil: moisture, surface roughness Vegetation: crop/forest type, biomass Snow: depth, density (water equivalent), wetness, grain dimension