Wideband Ocean Altimetry Using KU and K-Band Satellite Signals of Opportunity (SOOP)

Soon Chye Ho, Purdue University

Abstract

Precise measurements of ocean parameters are important for atmospheric and weather modeling. Hence, several methods have been developed over recent decades, including altimetry, scatterometry, and radiometry for remotely sensing parameters like Significant Wave Height (SWH), Sea Surface Height (SSH), Mean Wave Period (MWP), Sea Surface Salinity (SSS), tidal level, wind speed, and wind direction. These techniques have been demonstrated during a series of satellite missions, including TOPEX/Poseidon, Jason, and QuickSCAT, evolving from “pathfinder” or demonstration experiments to operational missions. This dissertation explores a technique for measuring ocean surface topography parameters using reflectometry and telecommunication signals in a bistatic configuration. This dissertation applies an ocean remote sensing method using Signals of Opportunity (SoOp), specifically reflected digital telecommunication satellite signals. The fundamental observation is the cross correlation waveform from the direct and reflected signal. Relationships are derived between the coherence time of the waveform and SSH of the sea surface. A proof-of-concept experiment has demonstrated that wideband (400 MHz) signals of opportunity (SoOp) transmitted in K and Ku-band from geostationary satellites can be used for coastal altimetry. An important finding from this experiment is that the full broadcast spectrum consisting of multiple digital channels can be processed as a single wideband signal source. An established error model for Global Navigation Satellite System interferometric altimetry (iGNSS-R) was shown to accurately represent the sea surface height (SSH) retrievals when evaluated using the full bandwidth. This experiment was conducted over a 72 hour period at Platform Harvest off the Pacific Coast. Co-located tide gauge and LiDAR measurements were used as in situ data. Two anomalies were observed in the experiment: 1. Multiple peaks in the cross correlation waveform from one polarization of Ku-band frequency. 2. Decrease in SNR from loss of a data channel. When the instances of multiple peaks were eliminated and the equivalent bandwidth recomputed using only the active channels, SSH error from these cases agreed well with the model prediction. Application of SoOp wideband altimetry will therefore require a monitoring capability to identify changes in the transmission spectrum, total power, and waveform shape, for quality control and setting an appropriate observation error covariance. The measurement precision from a satellite receiver is predicted to be between 4-6 cm using the error model. The last part evaluates the performance of altimetry measurements using the Cramer Rao Lower Bound and Root Mean Square bandwidth approaches. The full bandwidth model can well predict the overall precision of the path delay measurement in LHCP measurement. For K-RHCP measurement, after excluding the measurement data during spectrum transition period, the full bandwidth model can work well. SoOp altimetry with these signals may improve coastal measurements and increase the sampling and revisit rate through use of a constellation of small satellites.

Degree

Ph.D.

Advisors

Garrison, Purdue University.

Subject Area

Aquatic sciences|Biological oceanography|Environmental management|Mathematics|Physical oceanography

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