Retrieving significant wave height in the Indian Ocean near Visakhapatnam using Jason-2 altimeter data

Abstract

Five-parameter model (BETA5) has been used to derive significant wave height (SWH) using 20-Hz Jason-2/OSTM Ku band waveforms in the Bay of Bengal basin of the Indian Ocean near the Indian city of Visakhapatnam for the years 2010-2012. Majority of the waveforms are traditional ocean-like waveforms based on Brown model. Nevertheless, quite a few of them have shapes differing significantly from the Brown model. Historically, two standard methods have been used for waveform retracking. One is maximum likelihood estimator (MLE) with 4 parameters, i.e. MLE4 (OCEAN retracker), which uses analytical second-order Brown model and the second one using first-order Brown model is MLE with three parameters, i.e. MLE3. It has been found in the study that standard MLE retrackers are not appropriate for retracking the nontraditional waveforms. Estimated SWHs have been validated against SWH measured by a buoy located in the close proximity of Visakhapatnam. SWH from BETA5 retracker matches buoy-derived SWH quite well except for a positive bias. Also, the bias is less for SWH retrieved using BETA5 than using MLE retrackers. Quantitatively, at a distance of 8 km from the coast correlation coefficient between BETA5 retracked SWH and buoy measured SWH is 0.85 and the unbiased root mean square error (RMSE) of the retracked SWH is 0.26 m. These are better than the corresponding values for MLE3 and OCEAN retrackers.

Validation of Improved Significant Wave Heights from the Brown-Peaky (BP) Retracker along the East Coast of Australia

“…This results in the well-known problem that altimeter returned echoes are often contaminated by the coastal environment. Further improvement requires more advanced altimetry technology, such as the synthetic aperture radar (SAR) mode altimeter (e.g., CryoSat-2 and Sentinel-3A) and the Ka-band altimeter (e.g., SARAL/Altika), which both have shown excellent performance in coastal regions [10,18,[35][36][37][38][39].…”

“…According to the recommendations from previous studies [8,[16][17][18][19][20], we will only use Jason-1 along-track data within 50 km from the corresponding buoy. Table 1 lists information about the buoy, the ground tracks, distance between the buoy and track, and distance between the buoy and the coast.…”

Development of the wave spectrum of the northern region of the Bay of Bengal based on Indian National Centre for Ocean Information Services (INCOIS) moored buoy data

“…Seasonal and annual variations in the wave climate over the near shore waters off Puduchery, south western Bay of Bengal induced by monsoon and cyclone were studied by Glejin et al 26 . Chaudhary et al 27 The objective of the study is to investigate the characteristics of wave spectrum of northern region of the Bay of Bengal and its seasonal variation and derive formulae for the wave spectra and thus, to have a better understanding of the nature of the waves occurring in the region. The data used in the study were taken from the website of Indian National Centre for Ocean Information Service (INCOIS), covering the period from March, 2015 to February, 2016.…”