Calibration and Measurement Considerations for the Sea Winds Scatterometer Electronics Subsystem Support Equipment (SES SE)

The SeaWinds instrument is a microwave radar that measures near-surface wind velocity (both speed and direction) over the Earth¿s ice-free oceans. It uses a rotating dish antenna that produces two overlapping conical beams that measure the radar backscattering coefficient of the ocean¿s surface. Data produced will continue the data series started by the NASA Scatterometer (NSCAT), and will be made available near-real-time to operational meteorological agencies. The SeaWinds experiment is part of the Earth Observation System (EOS), designed to address global environmental changes. It will be launched into a near-polar sun-synchronous orbit on the second Japanese Advanced Earth Observation Satellite (ADEOS II) scheduled for flight in early 1999. The SeaWinds mission is planned to last three years. Raytheon E-Systems is designing and building the SeaWinds instrument Scatterometer Electronic Subsystem (SES) and the SES Support Equipment (SE) that will be used for calibrating the SES. Required measurement accuracies for the program are very demanding. The most stringent of these is the measurement of the SES transmitted power/receive gain (Pt*Gr) product. This parameter¿s absolute worst case error can be no more than 0.8 dB for all conditions of environment and test. In order to meet these requirements, design of the SE and selection of test equipment had to be carefully considered. The purpose of this paper is to describe the SeaWinds SE design, discuss the choice of instrumentation for the support equipment, and provide details of the error budgets for the SES Pt*Gr product.