Wave Measurements from Pulse Microwave Radar Tide Gauges

Abstract

Currently the NOAA Center for Operational Oceanographic Products and Services (CO-OPS) is transitioning the primary water level sensor at most NWLON stations from an acoustic ranging system to microwave radar altimeters. The use of the microwave radars presents the potential to provide real-time wave information at NWLON sites in support of navigational safety and ocean research applications. Radar sensors at tide stations may offer a low cost, convenient way to increase nearshore wave observational coverage throughout the U.S. In a previous study, we examined the performance from a pulse microwave radar and continuous wave frequency modulated (CWFM) radars [1]. While both types of radars tracked significant wave height well, the pulse radar had less success resolving high frequency wind wave energy and aliased low frequency energy. The CWFM radars were more successful, though more costly in both expenses and power. Here we present the results of a continuation of that field study, focusing on the comparison of wave height measurements from two pulse microwave radar water level sensors, the WaterLOG H3611 and the Endress and Hauser Micropilot FMR240. A nearby bottom acoustic wave and current sensor (AWAC) is used as a reference. Significant wave height measurements from both radar water level sensors compared well to reference AWAC measurements over the test period, however the WaterLOG radar does not adequately resolve wind wave energy in high frequency bands (0.1 Hz and above) and aliases energy towards the low frequency end of the spectrum. WaterLOG radar limitations are most apparent during times of high winds and locally developing seas. The E+H radar demonstrates greater capability to resolve those higher frequency energies while avoiding the low frequency aliasing issue observed in the WaterLOG. An overview of field setup and sensors will be presented, along with an analysis of performance capabilities of each radar sensor.