1. Estimation of Potential Evapotranspiration from Merged CERES and MODIS Observations Anand Inamdar & A. French Arid Land Agricultural Research Center (ALARC/ARS/USDA) 21881 North Cardon Lane Maricopa, AZ 85238 American Meteorological Society 89 th Annual Meeting, Phoenix AZ, Jan 12, 2009

2. Outline Satellite-based estimation of potential Evapotranspiration using the new generation of Earth Observation System (EOS) satellites; Approach: merge Clouds and Earth’s Radiant Energy System (CERES) and Moderate Resolution Imaging Spectroradiometer (MODIS) instruments data to estimate net surface radiation on 1 km scale; Implement MODIS narrowband to broadband conversion; Take advantage of the extensively developed and well- validated CERES TOA to surface flux algorithms and extend the same to MODIS high resolution multi- spectral data

3. Clouds and Earth’s Radiant Energy System (CERES) Broadband scanning radiometer Broadband scanning radiometer 0.3 – 5  m, 8 – 12  m and 0.3 – 50  m 0.3 – 5  m, 8 – 12  m and 0.3 – 50  m Single Scanner Footprint (SSF) includes instantaneous solar-reflected and Earth-emitted radiation from TOA to the Earth’s surface to study the role of clouds, aerosols and radiative fluxes in climate. Single Scanner Footprint (SSF) includes instantaneous solar-reflected and Earth-emitted radiation from TOA to the Earth’s surface to study the role of clouds, aerosols and radiative fluxes in climate.

4. SSF data contains one hour of instantaneous CERES data; CERES + High resolution Imager scene information; Number of cloud layers & cloud properties; Major SSF data: CERES FOV geometry, filtered and unfiltered TOA SW, LW and WN radiances, Imager statistics TOA radiances --  TOA flux values (based on imager scene types) TOA flux  surface flux (SW based on Li et al algorithm and LW based on Inamdar et al algorithm). Imager channels convolved with the CERES FOV: Combination of 5 channels consisting of 0.645, 0.858, 1.64, 3.792, 8.55, 11.03 and 12.02  m;

6. MODIS narrowband radiance  TOA broadband SW flux where I  represent imager radiance in channels 0.644, 0.858 and 1.64  m

8. Net SW surface flux (ΔF SW,SFC ) Based on Li et al (1993) algorithm relating the net flux at the surface in terms of TOA flux (F SW,TOA ), cosine of solar zenith angle (  and column precipitable water (w cm).

9. Correction for the aerosol (Masuda et al, 1995) implemented using climatological aerosol optical depth (0.55 mm) obtained from the Global Aerosol Climatology Project (http://www.gacp.giss.nasa.gov)

11. Downward LW Flux We employ a simplified form of the Longwave model A (Inamdar & Ramanathan) implemented in CERES SSF data.

13. Future Enhancements Use of additional MODIS channels; Use of additional MODIS channels; Convolution of MODIS channels with CERES FOV employing 1 km resolution PSF weights; Convolution of MODIS channels with CERES FOV employing 1 km resolution PSF weights; Implementation of scene-dependent Angular Distribution Models to convert MODIS-derived TOA radiances to broadband flux; Implementation of scene-dependent Angular Distribution Models to convert MODIS-derived TOA radiances to broadband flux; Better representation of aerosol effects; Better representation of aerosol effects; Use of GOES Imager VIS channel to perform temporal interpolation Use of GOES Imager VIS channel to perform temporal interpolation

14. Conclusions Examined schemes for estimation of net surface radiation from MODIS channels employing CERES broadband data for calibration; Examined schemes for estimation of net surface radiation from MODIS channels employing CERES broadband data for calibration; Study is restricted to the limited number of MODIS channels convolved with the CERES IFOV in the SSF data granule; Study is restricted to the limited number of MODIS channels convolved with the CERES IFOV in the SSF data granule; Results show potential for accurate satellite-based estimation of Evapotranspiration at high spatial and temporal resolution on a global scale. Results show potential for accurate satellite-based estimation of Evapotranspiration at high spatial and temporal resolution on a global scale.