scholarly journals Relative Navigation in LEO by Carrier-Phase Differential GPS with Intersatellite Ranging Augmentation

2013 ◽  
Vol 2013 ◽  
pp. 1-11 ◽  
Author(s):  
Alfredo Renga ◽  
Michele Grassi ◽  
Urbano Tancredi
Keyword(s):  
Synthetic Aperture Radar ◽  
Numerical Simulations ◽  
Carrier Phase ◽  
Synthetic Aperture ◽  
Relative Navigation ◽  
Next Generation ◽  
Differential Gps ◽  
Promising Technology ◽  
Gps Satellites ◽  
Noisy Measurements

Carrier-phase differential GPS (CDGPS) is a promising technology for accurate relative navigation in LEO formations of cooperating satellites, but navigation filter robustness against poor GPS geometry and noisy measurements has to be improved. This can be performed by augmenting the navigation filter with intersatellite local ranging measurements, as the ones provided by ranging transponders or GNSS-like systems. In this paper, an augmented CDGPS navigation filter is proposed for the formation of two satellites characterized by a short, varying baseline, relevant to next generation Synthetic Aperture Radar missions. Specifically, a cascade-combination of dynamic and kinematic filters which processes double-differenced code and carrier measurements on two frequencies, as well as local inter-satellite ranging measurements, is used to get centimeter-level baseline estimates. The augmented filter is validated by numerical simulations of the formation orbital path. Results demonstrate that the proposed approach is effective in preserving the centimeter-level accuracy achievable by a CDGPS-only filter also in the presence of a poor GDOP or a limited number of GPS satellites in view.

Estimating Potential Woody Biomass in Communal Savanna Woodlands from Synthetic Aperture Radar (SAR)

2012 ◽  
Vol 3 (1) ◽  
pp. 53-62 ◽  
Author(s):  
Charles Paradzayi ◽  
Harold J. Annegarn
Keyword(s):  
Synthetic Aperture Radar ◽  
Woody Biomass ◽  
Synthetic Aperture ◽  
Woody Vegetation ◽  
Differential Gps ◽  
Alos Palsar ◽  
Backscatter Intensity ◽  
Vegetation Class ◽  
The Mean ◽  
Aperture Radar

Recent developments in Synthetic Aperture Radar (SAR) technologies have shown their potential for assessing and quantifying above-ground biomass (AGB) at landscape levels in different biomes. This paper examines the application of full polarimetric data to retrieve information related to potential woody biomass in sparse communal savanna woodlands in southern Africa using the Advanced Land Observation Satellite’s Phased Array L-band Synthetic Aperture Radar (ALOS PALSAR). Woody vegetation classes were obtained from the unsupervised entropy/alpha Wishart classification of the full polarimetric ALOS/PALSAR data. A combination of Differential GPS and conventional surveying techniques was used for a field inventory survey to estimate plot-level biomass densities in Welverdiend communal woodlands of South Africa. Regression analysis was used to derive the logarithmic relationship between the sampled plot AGB densities and the mean backscatter intensity of the microwave signal, which is transmitted in the horizontal plane and received in the vertical plane (HV). The AGB density for each woody vegetation class is estimated by solving the logarithmic equation after extracting the mean HV backscatter intensity for the particular vegetation class. The potential woody biomass is estimated from the derived AGB densities and the areal extent of the respective woody vegetation classes.

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