Satellite measurements of solar radiation in the Yaqui Valley, northern Mexico

Abstract

Half-hourly estimates of solar radiation were obtained from satellite data for the Yaqui Valley in Sonora, Mexico for the period November 1998 to March 1999. Estimates were made on a 50 km grid using the Global Energy and Water-Cycle Experiment Surface Radiation Budget (GEWEX/SRB) algorithm applied with GOES-East data and, on a 4 km grid, using a high-resolution development of the GEWEX/SRB algorithm with GOES-West data. The resulting values were compared with field measurements made at two field sites. On average, using the presently specified calibration of the radiometers on the two satellites, the values derived from GOES-East data are 18% greater than field measurements, while those from GOES-West are 9% lower. If these systematic differences reflect the current poor calibration of the satellite sensors, the estimates obtained from each satellite may be corrected to agree with the surface data. After re-calibration, significant random differences between the hourly satellite estimates and surface observations remain because the satellite provides an instantaneous area-average estimate, while the field observation is a time-average single-point measurement. These discrepancies are reduced when daily-average values of solar radiation are compared. The error between the satellite and ground measurements is lower for the high-resolution estimates than it is for the low-resolution estimates, and there is an enhancement of spatial detail with the high-resolution data, making the latter preferable for hydrological applications. Previous research demonstrated the capacity for estimating potential evaporation in the area from daily-average solar radiation using a locally calibrated version of the Makkink equation. Locally relevant crop factors also have been derived for wheat and cotton.