Validation of Wave Spectral Partitions from SWIM instrument on-board
CFOSAT against In-situ Data
Abstract
The Surface Waves Investigation and Monitoring (SWIM) instrument onboard
the China France Oceanography Satellite (CFOSAT) can retrieve
directional wave spectra with a wavelength range of
70~500 m. This study aims to validate the partitioned
integrated wave parameters (PIWPs) from SWIM, including partitioned
significant wave height (PSWH), peak wave period (PPWP), and peak wave
direction (PPWD), against those from National Data Buoy Center (NDBC)
buoys. With quasi-simultaneous spectra from two NDBC buoys 13 km away
from each other near Hawaii, the methods of comparing PIWPs from two
sets of spectra were discussed first. After cross-assigning partitions
according to the spectral distance, it is found that wrong
cross-assignments lead to many outliers strongly impacting the estimate
of error metrics. Three methods, namely comparing only the best-matched
partition, changing the threshold of spectral distance during
cross-assignment, and maximum likelihood estimation of root-mean-square
error (RMSE) of PIWPs, were used to reduce the impact of potential wrong
cross-assignments. Using these methods, the SWIM PIWPs were validated
against NDBC buoys. The results show that SWIM performs well at finding
the spectral peaks of different partitions with the RMSE of PPWPs and
PPWDs of 0.9 s and 20{degree sign}, respectively, which can be a
useful complement for other wave observations. However, the accuracy of
PSWH from SWIM is not that good at this stage, probably because the high
noise level in the spectra impacts the result of the partitioning
algorithm. Further improvement is needed to obtain better PSWH
information.