VERIFYING SATELLITE MICROWAVE RAINFALL ESTIMATES OVER THE OPEN-OCEAN

Satellite rainfall estimates from a microwave emission-based algorithm by Wilheit et al, are verified using the noncontiguous rain gauge met hod incorporating monthly Pacific atoll rain gauge data. The results a re compared with those obtained using an infrared-based satellite algo rithm, the GOES precipitation index. Comparisons between satellite est imates with simple spatial averages of point rain gauge data are shown to be ineffective at identifying statistically significant difference s between the two algorithms due to substantial amounts of spatial sam pling error in the rain gauge spatial averages. By effectively reducin g this error, the noncontiguous rain gauge method reveals distinctive differences in the ability of each of the algorithms to accurately est imate monthly rainfall over the open ocean. The results indicate that the microwave algorithm, while slightly biased, is significantly less biased than the infrared, which tends to overestimate high rainfall va lues and underestimate low rainfall values. However, the random error associated with bath algorithms is essentially the same.