Analytic Descriptions of the Ionospheric Impact on Space-Based Synthetic Aperture Radar

Completed

Not Energy Related
Renewable Energy Sources(Bio-Energy, Other bio-energy)

Basic and strategic applied research

ENGINEERING AND TECHNOLOGY (Electrical and Electronic Engineering)

Not Cross-cutting

Professor PS Cannon
Electronic, Electrical and Computer Eng
University of Birmingham

Standard

EPSRC

08 March 2011

07 September 2014

42 months

£434,992

Info. & commun. Technol.

West Midlands

NC : ICT

Professor PS Cannon, Electronic, Electrical and Computer Eng, University of Birmingham

Dr D Belcher, University of Bath

Project Contact, Swedish Defence Research Establishment
Project Contact, QinetiQ Ltd
Project Contact, Workers Educational Association

Current space based observations of the Earth, whilst providing consistent and global coverage of land use, do not accurately measure forest biomass. This is because high frequency electromagnetic radiation (including X-band radar, optical and infra red sensors) measure scattering from surface features, such as leaves, and do not measure the biomass contained beneath. Although the situation is better with lower frequency C-band radar (such as Envisat) and even lower frequency L-band radar (such as PALSAR), the scattering that they measure still saturates at low levels of biomass. To overcome this limitation, longer wavelength (~1m, P-band) signals, which penetrate deeper into the forest, are needed. The backscatter from such radars saturate at higher levels of biomass, thus enabling accurate measurement. Low frequency SAR also has potential military applications, most notably as a counter to camouflage, concealment under foliage, and deception, and in planetary exploration missions.The overriding disadvantage of using long wavelengths, apart from antenna design issues due to their proportionally larger size, is the degrading impact of the ionosphere. The ionosphere is a highly variable and turbulent medium which at these frequencies primarily affects the phase of a radar signal with amplitude affects due to diffraction. The degrading effects are most prevalent at high and equatorial latitudes and in the evening sector. Judicious choice of the orbit may mitigate the ionospheric impact but this is not always possible for operational reasons, including the requirements of other payloads. PALSAR is an example of a satellite in an orbit which is affected by ionospheric turbulence as well as gradients.In this project, the generic problems identified above will be addressed by a three pronged attack. (a) The development of novel analytical expressions of the effect of the ionosphere on SAR imaging. (b) Comparison and verification of the analytic expressions through numerical simulation (facilitated through a full-diffraction parabolic-method). (c) Comparison and verification of the analytical expressions through comparison with experimental SAR images of known calibrated targets which have been imaged through the turbulent equatorial ionosphere.The analytic theory will be verified by a full simulation of the ionosphere that includes diffraction effects, ideally required for P-band frequencies and below. The experimental validation of our model will use L-band PALSAR imagery (made available by ESA), since there is no P-band SAR in orbit; for this, calibrated corner reflector targets will be used. To link analytic, numerical and experimental data we will need a measure of the TEC and ionospheric strength of turbulence. This will be provided through Global Positioning Satellite (GPS) measurements of signal phase. Further, we will utilize satellite beacon measurements of scintillation at 150 MHz and 400 MHz to link measurements at L-band (SAR and GPS)to frequencies most pertinent to a low frequency SAR. The measurements will be made in the equatorial region where the effects are largest.Once the analytic theory has been developed and verified, it will be applied to biomass measurement accuracy estimates and more generally to the design of SAR systems optimized to mitigate the ionosphere. Algorithmic developments and improvements will follow

06/12/10