Comparison of Near Coastal Significant Wave Height Measurements from SARAL/AltiKa with Wave Rider Buoys in the Indian Region

Abstract

Significant Wave Height (SWH) measurement data from the AltiKa Radar Altimeter (RA) for the first 13 cycles of satellite coverage are compared with the SWH from Wave Rider Buoys (WRB) located at nine stations along the Indian coast to assess the performance of the altimeter over the coastal region. AltiKa SWH observations within a 30-minute interval and 50 km distance from WRBs are found to be over estimated by 6%, the Root Mean Square Error (RMSE) is 0.36 m, the Scatter Index (SI) is 26%, and the correlation coefficient (r) is 0.91. Relaxing the distance criteria by 50 km leads to increase in RMSE and deterioration of r to 0.89. There is a marked difference in the statistics on the comparison pairs pooled separately for the buoys near west and east coasts, with the latter showing RMSE error 26% more than the former. The method of Cressman weights adopted to correct for the errors arising out of the temporal and spatial differences in altimeter and buoy data comparison pairs resulted in reduction of RMSE by 5% and 25%, respectively, for the 30-minute and 50 km criteria and 4% and 56% for the 30-minute and 100 km criteria.

Keywords:

• Comparison
• SARAL/AltiKa
• SWH
• Wave rider buoy

Acknowledgements

This study is a component of the science investigations carried out by the authors as a part of SARAL/AltiKa science team. We thank Director NRSC and CGM, RRSCs for their support and encouragement throughout this study. The authors thank INCOIS for buoy data provided through their website (www.incois.gov.in) and CNES for AVISO data through their website (www.aviso.oceanobs.com). Thanks are also due to the editor and the anonymous reviewers for their critical suggestions that helped to improve the quality of this manuscript.