Location of Repository

Sea state and rain: a second take on dual-frequency altimetry

By G.D. Quartly

Abstract

TOPEX and Jason were the first two dual-frequency altimeters in space, with both operating at Ku- and C-band. Each thus gives two measurements of the normalized backscatter, sigma0, (from which wind speed is calculated) and two estimates of wave height. Departures from a well-defined relationship between the Ku- and C-band sigma0 values give an indication of rain.<br/>This paper investigates differences between the two instruments using data from Jason's verification phase. Jason's Ku-band estimates of wave height are ~1.8% less than TOPEX's, whereas its sigma0 values are higher. When these effects have been removed the root mean square (r.m.s.) mismatch between TOPEX and Jason's Ku-band observations is close to that for TOPEX's observations at its two frequencies, and the changes in sigma0 with varying wave height conditions are the same for the two altimeters. Rain flagging and quantitative estimates of rain rate are both based on the atmospheric attenuation derived from the sigma0 measurements at the two frequencies. The attenuation estimates of TOPEX and Jason agree very well, and a threshold of -0.5 dB is effective at removing the majority of spurious data records from the Jason GDRs. In the high sigma0 regime, anomalous data can be cause by processes other than rain. Consequently, for these low wind conditions, neither can reliable rain detection be based on altimetry alone, nor can a generic rain flag be expected to remove all suspect data

Topics: GC
Year: 2004
OAI identifier: oai:eprints.soton.ac.uk:330
Provided by: e-Prints Soton

Suggested articles

Preview

Citations

  1. (1991). A Geosat altimeter wind speed algorithm and a method for altimeter wind speed algorithm development. doi
  2. (1988). A study of the effect of rain on Seasat radar altimeter data. doi
  3. (1997). Achieving accurate altimetry across storms: Improved wind and wave estimates from C-band. doi
  4. (2000). Changes in oceanic precipitation during the 1997-98 El NiƱo. doi
  5. (2003). Comparison of the Ku-band range noise level and the relative sea state bias of the Jason-1, TOPEX and POSEIDON-1 radar altimeters. doi
  6. (1998). Estimation of wind stress using dualfrequency TOPEX data. doi
  7. (1999). Global precipitation statistics from dual-frequency TOPEX altimetry. doi
  8. (1998). Identification of possible wave damping by rain using TOPEX and TMR data. doi
  9. (2003). Jason-1 geophysical performance evaluation. doi
  10. (2000). Monitoring and cross-calibration of altimeter 0 through dual-frequency backscatter measurements. doi
  11. (1991). NASA radar altimeter for the TOPEX/POSEIDON project. doi
  12. Oceanic Tech. doi
  13. (2000). On the gate-dependence of geophysical retrievals from the TOPEX altimeter. doi
  14. (2000). Precipitation detection by the TOPEX/Poseidon dual-frequency radar altimeter, TOPEX Microwave Radiometer, Special Sensor Microwave/Imager and climatological shipboard reports. doi
  15. (2003). Simultaneous ocean wave measurements by the Jason and Topex satellites, with buoy and model comparisons. doi
  16. (1994). The corrections for significant wave height and attitude effects in the TOPEX altimeter. doi
  17. (1995). The effects of rain on ERS-1 radar altimeter data. doi
  18. (1996). The effects of rain on Topex radar altimeter data. doi
  19. (1997). The effects of rain on TOPEX/POSEIDON altimeter data. doi
  20. (1994). TOPEX/POSEIDON mission overview. doi
  21. (2003). Validation of Envisat RA2 rain flag.
  22. (2002). Validation of TOPEX rain algorithm: Comparison with ground-based radar. doi

To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.