Monitoring Measurements from the Jason-1 Microwave Radiometer and Independent Validation with GPS

Abstract

The Jason-1 Microwave Radiometer (JMR) provides measurements of the wet troposphere content to correct the altimetric range measurement for the associated path delay. Various techniques are used to monitor the JMR wet troposphere path delays, with measurements of zenith troposphere content from terrestrial GPS sites used as an independent verification technique. Results indicate that an unexpected offset of approximately +4.1 ± 1.2 mm (drier) emerged in the JMR measurements of wet path delay between cycles 28–32 of the Jason-1 mission, and that the measurements may be drifting at a rate of approximately −0.5 mm/year. These anomalies are shown to be caused by a −0.7 K offset in 23.8 GHz brightness temperatures between cycles 28–32, and a 0.16 ± 0.04 and −0.45 ± 0.08 K/year drift in the 18.7 and 34.0 GHz brightness temperatures, respectively. Intercomparison of the 3-Hz JMR brightness temperature measurements show that they have been drifting with respect to each other, and that a dependence on yaw-steering regime is present in these measurements. An offset of 0.5 m/s between cycles 28–32 and a drift of approximately 0.5 m/s/year in the JMR wind speed measurements is also associated with these anomalies in the 1-Hz brightness temperatures. These errors in JMR wind speeds presently have a negligible impact on the retrieved JMR path delays.

Keywords:

• microwave radiometer
• GPS
• satellite altimetry
• wet troposphere

Acknowledgments

The authors would like to thank the reviewers for their helpful comments. We would also like to thank Jason Science Data Team at JPL, led by A. Badea, for providing us with the JMR Level 1 data in a timely manner. The work described in this article was performed at the Jet Propulsion Laboratory, California Institute of Technology under a contract with the National Aeronautics and Space Administration.

Notes

*The difference column is the difference between the average from cycles 35–50 with the average from cycles 10–25. Values in ()'s show the standard deviation. The combined estimate of the cycle 28–32 offset is derived from the weighted average of the four differences that include the JMR. Units are mm.

*The difference column is the difference between the average from cycles 35–50 with the average from cycles 10–25. ND1, ND2, and ND3 indicate the noise diode 1, 2, and 3 congurations. Values in ()'s show the standard deviation. Units are K.