CYGNSS Surface Wind Validation over the Tropical Ocean Using Moored Buoy Observations

Surface wind plays a crucial role in many local/regional weather and climate processes and helps to shape the global weather-climate system, through the exchanges of energy, mass and momentum across the Earth’s surface. However, there is a lack of consistent observations with continuous coverage over the tropical ocean. The recently launched NASA Cyclone Global Navigation Satellite System (CYGNSS) mission is a constellation of eight small spacecrafts that remotely sense near surface wind speed over the tropical ocean with high sampling rates both temporally and spatially. CYGNSS measurements are thought to be less sensitive to heavy rain or cloud as each spacecraft equipped with the L-band (~1.6 GHz) sensor. In the current phase of the mission, validation is a critical task, and over ocean it is typically challenging due to a variety of environmental and geophysical conditions. This analysis takes advantage of the Tropical Moored Buoy Arrays to quantitatively characterize and validate the CYGNSS derived winds over the open oceans, including the tropical Indian, Pacific, and Atlantic Oceans. The quality of surface winds is further assessed under different precipitation conditions characterized by the buoy rain gauges. The validation results show that the uncertainty in CYGNSS derived wind speed for these tropical buoy comparison is below 2 m s^-1root mean squared difference, indicating that CYGNSS is meeting its NASA science mission Level-1 uncertainty requirement related to wind speeds < 20 m s^-1. The CYGNSS winds compare fairly well with buoy observations in the presence of rain, though at low wind speeds CYGNSS measurements may be somewhat affected by the rainfall. The comparison indicates the potential utility of the CYGNSS surface wind product, which in turn may help to unravel the complexities of air-sea interaction in regions that are relatively under-sampled by other measurement systems. Details about the validation methods and challenges of evaluating remotely sensed surface wind measurements will be addressed in this presentation.