Hong Zeng Tseng

Application of retracked satellite altimetry for inland hydrologic studies

We explored the application of satellite radar altimetry for the monitoring of small inland bodies of water and hydrologic studies using a water-detection algorithm, optimally retracked TOPEX/POSEIDON data at 10-Hz sampling, and investigated the use of radar backscatter to improve land cover classification. The procedure was demonstrated over Manitoba and south-western (SW) Ontario, and the Amazon River Basin study regions. Compared with an L-band synthetic aperture radar data generated water-land cover mask, the water-detection algorithm detected more water points over the Amazon basin. High correlation of 0.98 between the retracked 10-Hz altimetry and the gauge measurements in Manitoba confirmed that the retracked TOPEX data are more accurate than the non-retracked data, and with higher along-track spatial resolution by virtue of its higher sampling at 10 Hz.

Lake Surface Height Calibration of Jason-1 and Jason-2 Over the Great Lakes

This study presents results of Jason-1 (J1) and Jason-2 (J2) radar altimetry absolute calibration (cal/val) over the Marblehead lake water level gauge, with an aid of a GPS buoy, in Lake Erie, the Great Lakes, in North America. The altimeter bias is estimated using the height difference between the altimeter lake surface height and the in situ data in each altimeter 10-day repeat cycle. The altimeter bias estimates for J1 are 81 ± 2 and 70 ± 2 mm for Geophysical Data Record (GDR) Versions ‘B’ and ‘C’, respectively, and 148 ± 5 mm (GDR) and 147 ± 7 mm (IGDR) for J2, respectively. The bias estimates are slightly smaller compared with estimates at other dedicated calibration sites such as the Harvest Platform, the Corsica Site, and the Bass Strait site due in part to the effect of the sea state bias. The J2-to-J1 relative bias determined in the tandem mode over Lake Erie is 84 ± 28 mm, which agrees well with the results from the global analysis and the dedicated sites aforementioned.

Branco river stage gradient determination and Amazon hydrologic studies using GPS water level measurements

This study presents the result of a demonstration of Global Positioning System (GPS) hydrologic studies in a remote area. A GPS campaign was conducted using a GPS-equipped vessel and a GPS buoy to measure water level along Rio Branco, a tributary of the Amazon. The GPS water level data agree well with river gauge data and with ENVISAT radar altimeter measurements. The GPS-estimated river stage gradient of Rio Branco is 5.75 ± 0.48 cm/km with 99% confidence, which is higher than previous estimates. This result also agrees well with ENVISAT altimetry results.

Modal Frequency Identification of Stay Cables with Ambient Vibration Measurements Based on Nontarget Image Processing Techniques

Conventional sensors, such as the accelerometers and velocimeters, have been generally adopted to conduct the vibration measurements of stay cables for the identification of their dynamic parameters. Even though these contact sensors are able to obtain accurate measurements, the installation of such devices may require substantial efforts. A simple digital videogrammetric technique without using any artificial target is developed in this study to perform the ambient vibration measurements of stay cables for the subsequent identification of cable frequencies. This method significantly simplifies the image processing procedures by exploiting the straight boundary of cable to determine the midpoint of its edge line for serving as a convenient pseudo target. Demonstrated by the on-site measurements for three different cables selected from Chi-Lu Bridge, it is shown that this nontarget technique equipped with a customer grade camcorder and an ordinary tripod placed on the bridge deck can attain the same order of accuracy for cable frequency identification as that of high-resolution velocimeters. Both the vertical and transverse displacements of cable were measured under the ambient vibration amplitudes in the order of 0.5 mm and 0.2 mm, respectively. Based on this study, it is proved that the practical application of a nontarget videogrammetric technique to the cables of long-span cable-stayed bridges is not only feasible but also advantageous in many aspects.