On Signal Modeling of Moon-Based Synthetic Aperture Radar (SAR) Imaging of Earth

Abstract

Abstract:The Moon-based Synthetic Aperture Radar (Moon-Based SAR), using the Moon as a platform, has a great potential to offer global-scale coverage of the earth's surface with a high revisit cycle and is able to meet the scientific requirements for climate change study. However, operating in the lunar orbit, Moon-Based SAR imaging is confined within a complex geometry of the Moon-Based SAR, Moon, and Earth, where both rotation and revolution have effects. The extremely long exposure time of Moon-Based SAR presents a curved moving trajectory and the protracted time-delay in propagation makes the "stop-and-go" assumption no longer valid. Consequently, the conventional SAR imaging technique is no longer valid for Moon-Based SAR. This paper develops a Moon-Based SAR theory in which a signal model is derived. The Doppler parameters in the context of lunar revolution with the removal of 'stop-and-go' assumption are first estimated, and then characteristics of Moon-Based SAR imaging's azimuthal resolution are analyzed. In addition, a signal model of Moon-Based SAR and its two-dimensional (2-D) spectrum are further derived. Numerical simulation using point targets validates the signal model and enables Doppler parameter estimation for image focusing.

Constructing a High-Accuracy Geometric Model for Moon-Based Earth Observation

“…A(t+∆t 1 For the sake of light time effect, the 'stop-go' hypothesis is no longer valid [18,52]. The SAR baseband signal of a point target echo after demodulation can be written as [39,53]: In SAR footprint geolocation, we need two targets to determine the three pointing angles.…”

“…The angular aberration effect almost gives no impact on range history, but the light time will cause slight changes in both transmitting and receiving propagation range. The real range history should be the sum of (I) transmitting [18]. In airborne SAR and low earth orbit SAR imaging, the range history is approximated to (III) + (III).…”

“…In airborne SAR and low earth orbit SAR imaging, the range history is approximated to (III) + (III). In reference [18], it is approximated to (III) + (IV). The differences between (III) + (III) and (I) + (II) reach 44.41 m, 34.12 m, and 7.90 m within a 10-min synthetic aperture when the target is put from low latitude to high latitude places ( Figure 13).…”

“…Recently, a simplified geometric model is widely used for spatial and temporal scope analysis [11,12] and the simulation of earth's outgoing radiation [13][14][15]. The moon-based SAR imaging geometry is also improved [16][17][18]. However, for the mission design of moon-based Earth's radiation budget measurement and moon-based SAR imaging simulation, the model is still made with too much simplification.…”

A Compensation Method for Airborne SAR with Varying Accelerated Motion Error

“…Space-borne and airborne synthetic aperture radar (SAR) can work well day-and-night and weather-independently [1][2][3]. With high resolution image production, SAR is widely applied in remote sensing applications, e.g., Earth observation, marine surveillance, earthquake and volcano detection, interferometry, and differential interferometry.…”