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 Experi- ment 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 satel- lites, 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.