urn:nasa:pds:context:instrument:mrffr.ch1-orb 1.0 1.7.0.0 Product_Context 2016-10-01 1.0 extracted metadata from PDS3 catalog and modified to comply with PDS4 Information Model urn:nasa:pds:context:instrument_host:spacecraft.ch1-orb::1.0 instrument_to_instrument_host McKerracher, P.L., J.R. Jensen, H.B. Sequeira, R.K. Raney, R.C. Schulze, D.B.J. Bussey, B.J. Butler, C.D. Neish, M. Palsetia, G.W. Patterson, P.D. Spudis, B.J. Thomson, and F.S. Turner, Mini-RF calibration, a unique approach to on-orbit synthetic aperture radar system calibration, 41st Lunar and Planetary Science Conference, Abstract #2352, The Woodlands, Texas, March 2010. reference.MCKERRACHERETAL2010 MINI-RF FORERUNNER Radio-Radar not applicable not applicable Abstract: ========= Mini-RF is a side-looking synthetic aperture radar (SAR) instrument that is flying on the Chandrayaan-1 spacecraft. Chandrayaan-1 is an Indian Space Research Organisation (ISRO) lunar orbiter. Mini-RF operates in two modes, SAR mode and a nadir-looking scatterometry mode. Scientific Objectives: ====================== The primary scientific objectives of the Mini-RF Forerunner mission is to search for water-ice deposits in the north and south polar regions of the Moon. It will search for anomalous radar reflectivity signatures (high albedo and high circular polarization ratio) that can differentiate volumetric water-ice deposits from the more typical anhydrous lunar surface material. As an additional scientific objective, the Mini-RF mission will characterize the lunar surface roughness at radar wavelength scales. Calibration: ============ Amplitude calibration --------------------- The Mini-RF radar data product is comprised of the amplitude (or magnitude squared) of the H and the V channels of the dual-polarized receiver, and also the cross-product of the complex H and V amplitudes. These data are necessary and sufficient to form the 2x2 coherency matrix of the backscattered field, which is alternatively represented by the Stokes parameters, four real numbers. The first Stokes parameter represents the total backscattered power. This can be scaled to the normalized reflectivity sigma-zero only if the end-to-end transformation of the radar is calibrated absolutely. The starting point for this scaling is the set of pre-flight system data, coupled with in-flight specifics such as incidence and altitude. During the mission, absolute calibration will be up-dated by imaging a lunar area whose reflectivity is well known from Earth-based radar observatories. However, most lunar science measurements depend on ratios of the Stokes parameters, for which absolute amplitude calibration is not required. Rather, gain balance between the H and the V channels is the key objective. Relative calibration consists of evaluating the corrective scaling constant of the H amplitude relative to the V amplitude. Calibration references (noise, tone, and chirp) are included at the beginning and end of each data take to assist relative amplitude calibration. During the mission, relative calibration will be up-dated by radar coverage of the lunar surface at nadir, from which the observed backscatter should have identical amplitudes seen through both the H and the V channels. Any difference can be inverted to evaluate the relative amplitude calibration constant. In addition, the mission plan calls for relative amplitude calibration through a cooperative transmission and reception between the spacecraft and an Earth-based radar observatory. These data will be posted on the PDS when available. (If more specific information is needed, please consult the Mini-RF Calibration Plan [MCKERRACHERETAL2010].) Phase calibration ----------------- The Mini-RF radar data product is comprised of the amplitude (or magnitude squared) of the H and the V channels of the dual-polarized receiver, and also the cross-product of the complex H and V amplitudes. The cross-product is one representation of the phase to be calibrated. These data are necessary and sufficient to form the 2x2 coherency matrix of the backscattered field, which is alternatively represented by the Stokes parameters, four real numbers. The first Stokes parameter is the total backscattered power (see Amplitude Calibration). Under the operational assumption that the radar transmits circular polarization, the relative phase (in the cross-product) is central to the third and the fourth Stokes parameter. Relative phase calibration consists of evaluating the corrective phase rotation constant of the H complex amplitude relative to the V complex amplitude such that the average phase difference between them is +/-90 degrees (whose sign depends on whether right- or left-circular polarization was transmitted) under the condition that the average reflecting surface is specular. The starting position for relative phase calibration is the set of pre-flight system data, coupled with in-flight measurements based on the radar's calibration references (see Amplitude Calibration). During the mission, relative phase calibration will be up-dated by radar coverage of the lunar surface at nadir, from which the observed averaged backscatter should have known relative phase between the H and the V channels. Any difference can be inverted to evaluate the relative phase rotation calibration constant. In addition, the mission plan calls for relative phase calibration through a cooperative transmission and reception between the spacecraft and an Earth-based radar observatory. These data will be posted on the PDS when available. (If more specific information is needed, please consult the Mini-RF Calibration Plan.) Operational Modes: =========================== The Mini-RF instrument has two modes: SAR and Scatterometry. Sensors: ========== The radar is to prove the feasibility of a 10-kg class instrument in lunar orbit to support high-quality imaging data collection. Electronics: ============ The Mini-RF assembly consists of two sections, the antenna (a passive array of H and V elements, of about 1 square meter area), and electronics (packaged in three individual sub-assemblies).