Engineering topics

Li, F.-K.

Publications and source records attributed to Li, F.-K..

3 records

NASA NTRS1986

Radar backscatter measurement accuracies using digital Doppler processors in spaceborne scatterometers

The normalized standard deviation, Kp, of radar backscatter measurements using digital Doppler processors in spaceborne scatterometers is derived. The Kp expression for analog Doppler filter processors, such as that used in the Seasat scatterometer is shown to be a special case of the derived Kp expression. A connection to Welch's (1967) power spectrum estimation rsults is also made. Tradeoff studies in digital filter design such as hardware complexity, computational speed, and system performance can be performed based on this Kp expression. A current application in the design of the NASA scatterometer to be flown in 1990 is discussed. This derivation should be useful for system design and analysis of other radar remote-sensing instruments.

Chi, C.-Y.↗

NASA NTRS1985

Doppler parameter estimation for spaceborne synthetic-aperture radars

Problems in the determination of Doppler parameters for spaceborne synthetic-aperture radar (SAR) data processing are examined. The degradations in image quality due to errors in these parameters are summarized. It is shown that these parameters can be estimated using accurate spacecraft ancillary data. In cases where such data are not available, two techniques are proposed to estimate these parameters using the coherent radar return. These techniques were tested with the Seasat SAR data and the test results demonstrate that the accuracies achieved exceed the system performance requirements. Possible applications of these techniques in other areas of SAR data utilization are briefly discussed.

Li, F.-K.↗

NASA NTRS1983

Comparison of several techniques to obtain multiple-look SAR imagery

In order to improve image interpretability when SAR imagery is contaminated by coherent speckle noise, multiple look images are often generated. The performance levels of techniques for the generation of such multiple look imagery are presently assessed, with attention to the detailed impulse responses and signal-to-speckle noise ratios obtainable. The speckle-reduction technique considered are those of the discrete mixed integrator and the image domain filter. It is found that, by using several types of image domain filters, the signal-to-speckle noise ratio can be improved over the conventional discrete mixed integrator method's results while maintaining the equivalent rectangular resolution constant.

Li, F.-K.↗