Browsing by Author "Hwang, CheinWay"

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A multi-subwaveform parametric retracker of the radar satellite altimetric waveform and recovery of gravity anomalies over coastal oceans
(2010-04-01)
Guo JinYun
;
Gao YongGang
;
Hwang, CheinWay
;
Sun JiaLong
;
土木工程學系
The quality of satellite radar altimetric data is very important in studies of geodesy, geophysics, and oceanography. Over coastal oceans, altimeter waveforms are contaminated by the terrain and physical environments so that the accuracy of altimeter data is lower than that over open oceans. Here we develop a new multi-subwaveform parametric retracker (MSPR) to improve the quality of altimeter data for the recovery of gravity anomaly in coastal oceans. The least squares collocation method is used to recover the residual gravity anomaly over the coastal water from altimetric data. The waveform data records from Geosat/GM around Taiwan Island are practically retracked with MSPR. When compared with the Taiwan geoid height, the results retracked by MSPR are more accurate than those retracked by the well-known beta-5-parmeter method and from the geophysical data records (GDRs). The gravity anomalies over Taiwan coastal waters are calculated from the retracked altimeter data with the least squares collocation. When we compared gravity anomalies computed using altimeter GDRs with the ship-borne gravity data over Taiwan coastal ocean, we found that the results from retracked data are more accurate than those from GDRs.
A multi-subwaveform parametric retracker of the radar satellite altimetric waveform and recovery of gravity anomalies over coastal oceans
(2010-04-01)
Guo JinYun
;
Gao YongGang
;
Hwang, CheinWay
;
Sun JiaLong
;
土木工程學系
The quality of satellite radar altimetric data is very important in studies of geodesy, geophysics, and oceanography. Over coastal oceans, altimeter waveforms are contaminated by the terrain and physical environments so that the accuracy of altimeter data is lower than that over open oceans. Here we develop a new multi-subwaveform parametric retracker (MSPR) to improve the quality of altimeter data for the recovery of gravity anomaly in coastal oceans. The least squares collocation method is used to recover the residual gravity anomaly over the coastal water from altimetric data. The waveform data records from Geosat/GM around Taiwan Island are practically retracked with MSPR. When compared with the Taiwan geoid height, the results retracked by MSPR are more accurate than those retracked by the well-known beta-5-parmeter method and from the geophysical data records (GDRs). The gravity anomalies over Taiwan coastal waters are calculated from the retracked altimeter data with the least squares collocation. When we compared gravity anomalies computed using altimeter GDRs with the ship-borne gravity data over Taiwan coastal ocean, we found that the results from retracked data are more accurate than those from GDRs.
On temporal-spatial distribution of backscatter coefficients over China determined by TOPEX/Poseidon mission
(2012-12-01)
Guo JinYun
;
Yang Lei
;
Liu Xin
;
Hwang, CheinWay
;
Yang Hong
This paper deals with the backscatter coefficients known as sigma0 at Ku band and C band based on the GDR-M (Merged Geophysical Data Record) of TOPEX/Poseidon (T/P) through Jan. 1993 to Dec. 2004 over land surface of China. After smoothing and interpolating the backscatter coefficients for both bands, we achieve the 5'x5' grid data and the time series of backscatter coefficients in 12 years. The spatial distribution of sigma0 over typical areas (wetland, desert, mountainous area, agriculture base, etc.) of Chinese territory is analyzed and discussed. The fast Fourier transformation (FFT) is used to detect the cycles of seasonal variations of sigma0 time series and gives that the annual period is the major cycle. Meanwhile a semiannual period is also found in some places. We use the least squares method on both periods and find that the amplitude of annual period is obviously greater than that of semi-annual period. The relationship among the anomalousness of time series, variations of environment and climate change, and the serious natural calamity (flood, drought) is also discussed. Data of topography slope extracted from SRTM are used to do correlation analysis with the backscatter coefficients in parts of China to quantify the impact of slope on backscatter coefficients in Ku and C bands, and the results show that they all have a negative correlation but the magnitudes are different in different places with different coverages. Such as the area of Liaoning and Jilin has the maximum correlation -0.56, the Taklimakan Desert has the minimum correlation -0.11, and the other places commonly have correlations in (-0.3, -0.5).