MEO SAR: System Concepts and Analysis

Abstract

Existing microwave remote sensing instruments used for Earth observation face a clear tradeoff between spatial resolution and revisit times at global scales. The typical imaging capabilities of current systems range from daily observations at kilometer-scale resolutions provided by scatterometers to meter-scale resolutions at lower temporal rates (more than ten days) typical of synthetic aperture radars (SARs). A natural way to fill the gap between these two extremes is to use medium-Earthorbit SAR (MEO-SAR) systems. MEO satellites are deployed at altitudes above the region of low Earth orbits (LEOs), ending at around 2000 km and below the geosynchronous orbits (GEOs) near 35 786 km. MEO SAR shows a clear potential to provide advantages in terms of spatial coverage, downlink visibility, and global temporal revisit times, e.g., providing moderate resolution images (some tens of meters) at daily rates. This article discusses the design tradeoffs of MEO SAR, including sensitivity and orbit selection. The use of these higher orbits opens the door to global coverage in one-to two-day revisit or continental/oceanic coverage with multidaily observations, making MEO SAR very attractive for future scientific missions with specific interferometric and polarimetric capabilities.

A Remote Carrier Synchronization Technique for Coherent Distributed Remote Sensing Systems

“…This transfer function is used to obtain the phase transfer function from the master oscillator phase 0 to the slave recovered phase reference out . This relation is found with the two signals transmitted to the follower node and retrieved in the phases 3 This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication.…”

System Design and Analysis for Energy-Efficient Passive UAV Radar Imaging System using Illuminators of Opportunity

“…The proposed energy-efficient passive UAV SAR utilizes transmitters of opportunity to illuminate the target scene. The potential illuminators can be flexibly chosen from satelliteborne SAR (LEO-SAR and future GEO/MEO-SAR [15], [16]), global navigation satellite system (GNSS) or groundbased stationary commercial illuminators (e.g., FM radio and DVB-T) according to their beam coverage and signal characteristics. The UAV platform passively receives the echo signal reflected from the target scene and achieves bistatic SAR imaging at a ground-based processing station.…”

“…In Table I, the TerraSAR-X satellite is assumed for LEO-SAR, of which the orbit altitude is 514km [14]. According to the current literature, the orbit altitude of MEO-SAR is set as 5,952km and high inclination GEO-SAR is considered in the simulation [15], [16]. The finest ρ g r are 0.5m, 1.72m and 1.5m and the ground azimuth resolution ρ g a are 0.73m, 1.15m and 1.19m for the simulated LEO-SAR, MEO-SAR and GEO-SAR illuminator, respectively.…”

“…In recent years, various aspects of SAR technology have been extensively studied, including bi/multi-static SAR [4]- [6], interferometry and polarimetry measurement [7]- [9], data focusing methods [10], [11] and moving target indication [12], [13]. Moreover, SAR sensors can be mounted on different platforms in order to satisfy distinct remote sensing and mission requirements, including spaceborne [14]- [16], airborne [17], [18] and missile-borne [19]- [21] platforms.…”

An Improved Equivalent Squint Range Model and Imaging Approach for Sliding Spotlight SAR Based on Highly Elliptical Orbit

“…Due to the low orbit altitude of LEO SAR, the large coverage and observation cannot be realized. In addition, although the orbital height of MEO SAR [7,8] and GEO SAR has been improved, it can realize observation imaging in a large area and continuous observation in local hot spot area. However, the engineering cost is too high because it only takes a period of the whole orbit period time to fulfill observation requirements at high latitudes.…”