In-Orbit Performance of the Constellation of CYGNSS Hurricane Satellites

Abstract

The NASA Cyclone Global Navigation Satellite System (CYGNSS) constellation of eight satellites was successfully launched into low Earth orbit on 15 December 2016. Each satellite carries a radar receiver that measures GPS signals scattered from the surface. Wind speed over the ocean is determined from distortions in the signal caused by wind-driven surface roughness. GPS operates at a sufficiently low frequency to allow for propagation through all precipitation, including the extreme rain rates present in the eyewall of tropical cyclones. The spacing and orbit of the satellites were chosen to optimize frequent sampling of tropical cyclones. In this study, we characterize the CYGNSS ocean surface wind speed measurements by their uncertainty, dynamic range, sensitivity to precipitation, spatial resolution, spatial and temporal sampling, and data latency. The current status of each of these properties is examined and potential future improvements are discussed. In addition, examples are given of current science investigations that make use of the data.

A Study on Assimilation of CYGNSS Wind Speed Data for Tropical Convection during 2018 January MJO

“…In this study, a few quality control steps were applied to the Level 2 CYGNSS data v2.1. Data with the range corrected gain below 3 and the zenith sun angle lower than zero were removed to Previous studies found that CYGNSS measurements during TC overpasses can help in finding the correct center location, estimating the intensity, and constructing the wind distribution within the TC [40,47,48]. Hoover et al [46] also showed that synthetic CYGNSS data may be used to monitor westerly wind burst (WWB) events during MJO events.…”

“…The FDS is appropriate for most conditions, while the YSLF data can be used typically for the inner core of TCs. YSLF GMF was developed for conditions when the long-wave portion of the sea state has not responded fully to the local surface winds [40,41]. Figure 2 displays the sample data of the CYGNSS v2.1 YSLF (Figure 2a) product around 1500 UTC, and FDS product over-plotted on GPM IMERG rainfall ( Figure 2b) at around 1500 UTC, and the ASCAT wind speed ( Figure 2c) at 1448 UTC on 7 January 2018.…”

“…Unfortunately, due to data quality issues, Cui et al [14] were only able to assimilate CYGNSS v2.0 fully developed seas (FDS) data, which greatly underestimates the wind field within deep convection regions related to TCs. A recent study (Ruf et al [40]) indicated that, with a number of improvements to the data calibration, v2.1 is of much better quality than the previous version; this is especially true for the young seas/limited fetch (YSLF) product. Ruf et al [41] calculated the root-mean-square (RMS) difference between CYGNSS v2.0 YSLF data and Stepped Frequency Microwave Radiometers (SFMRs) data onboard the NOAA P-3 aircraft in and near hurricanes.…”

“…For wind retrievals above 20 m s −1 , the RMS was 5.01 m s −1 when the uncertainty of the SFMR measurements was removed. When CYGNSS v2.1 YSLF data were evaluated, Ruf et al [40] indicated that this RMS value had been reduced to 3.2 m s −1 . In the current study, we examined the assimilation of both FDS and YSLF v2.1 wind speed products.…”

Geolocation, Calibration and Surface Resolution of CYGNSS GNSS-R Land Observations

“…The launch of the NASA Cyclone GNSS (CYGNSS) mission in Dec 2016 marked a significant opportunity to further validate and develop GNSS-R land applications. The primary mission of the eight satellite CYGNSS constellation is to measure ocean near surface winds for hurricane research [5]. However, multiple studies have recently demonstrated the use of CYGNSS land observations in surface water monitoring applications, including flood inundation [6] and near surface soil moisture [7,8].…”