Ohio State University. Division of Geodetic Science
Abstract
This research is conducted under the supervision of Dr. C.K. Shum, Professor of
Geodetic Science, School of Earth Sciences, The Ohio State University. The research
results documented in this report resulted in a PhD Dissertation. NASA and CNES
provided the TOPEX/POSEIDON (Geophysical Data Record and Sensor Data Record,
GDR and SDR) data products; LEGOS, USDA/NASA/GSFC provided high-level radar
altimetry data products; ANA Brazil, and Environment Canada provided the stage gauge
data used for this research. This research is supported by grants from NSF’s Hydrology
Program (EAR-0440007) and NGA’s NURI Program (HM1582-07-1-2024), and the
study was conducted with the objective to contribute to the Climate, Water, and Carbon
Program at The Ohio State University.Satellite radar altimetry, which is originally designed to measure global ocean surface
height, has been applied to inland surface water hydrologic studies. We have developed a
water-detection algorithm based on statistical analysis of decadal TOPEX/POSEIDON height
measurement time series, used the backscatter coefficient to classify the inland surface
properties, and the 10-Hz (corresponding to an along track spatial resolution of 700m) radar
waveform-retracked TOPEX data, to be able to observe small (<300Km2) inland bodies of
water for hydrologic studies. We applied the algorithm to the selected study regions in
Manitoba and northwestern (SW) Ontario, Canada, Amazon River Basin, and southwestern
Taiwan. Finally we studied the application of TOPEX altimetry to the 1997 Red River flood
monitoring. For the study regions in western Manitoba, the correlation coefficient between
stage and TOPEX altimetry data in the large Lakes reaches 0.98 using the 10-Hz retracked
data, thus verifying the validity and accuracy of the satellite measurement. The importance of
the waveform retracking for the inland water applications is validated by the improvement of
the correlation coefficients from 0.34 to 0.87 before and after retracking. We detected the
bodies of water, which are otherwise missed by using the original 1-Hz data from the
Geophysical Data Records, and illustrated that a higher spatial resolution could be achieved
using the individual 10-Hz retracked data. In the Amazon River Basin, the capability of the
water-detection algorithm is compared with the use of a high water level mask generated by
SAR and other data with a spatial resolution of 100m. It is shown that the algorithm could
detect the bodies of water, which are missed by the mask primarily because that the
frequency of water fluctuation is more than twice a year at some locations. The bodies of
water detected only by the algorithm are confirmed using the detailed local hydrological
maps in 3 tested regions. The retrieved water height over the small (<300Km2) body of water
was compared with the nearby stage measurement and showed good seasonal agreement. In
the southwest Taiwan, the monthly variation of 10-Hz AGC from 1992 to 2002 were
examined, it is found that the high AGC values could be used to indicate inundated area. We
detected the annual and semi-annual variations from the 10-Hz AGC and 10-Hz retracked
water height time series, which are attributable to two rainy seasons per year in the study
region. For the study of the 1997 Red River flood, we compared the geographic distribution
of 0 σ0 before, during and after the 1997 flood and found the high 0 σ0 values (>35dB)
indicate the inundated regions. In addition, the comparison of the geographically distributed
0 σ0 during Winter, Spring, Summer and Autumn of 1997 showed that the low 0 σ values
(<10dB) indicate snow coverage. The retrieved water height measurements in the flooded
regions are compared with the nearby USGS stage measurements and showed good
agreements. The comparison of 10-Hz individual retracked measurements with the 1-Hz nonretracked
height measurements confirmed the importance of the retracked data (with higher
spatial variations) in the flood monitoring. Using 0 σ0 and the retrieved water height
measurements, we detected the 1997 flooded regions include the Red River Basin of the
North in North Dakota and in western Minnesota, the upper Mississippi River Basin in
Minnesota, the Missouri River Basin in southern North Dakota and in South Dakota. The
observed flood extents from TOPEX agree well with and complement the USGS stage gauge
records