Abstract
Near-space, defined as the region between 20 km and 100 km, offers many new capabilities that are not accessible to low earth orbit (LEO) satellites and airplanes, because it is above storm and not constrained by either the orbital mechanics of satellites or the high fuel consumption of airplanes. By placing radar transmitter/receiver in near-space platforms, many functions that are currently performed with satellites or airplanes could be performed in a cheaper way. Inspired by these advantages, this paper introduces several near-space vehicle-based radar configurations, such as near-space passive bistatic radar and high-resolution wide-swath (HRWS) synthetic aperture radar (SAR). Their potential applications, technical challenges and possible solutions are investigated. It is shown that near-space is a satisfactory solution to some specific remote sensing applications. Firstly, near-space passive bistatic radar using opportunistic illuminators offers a solution to persistent regional remote sensing, which is particularly interest for protecting homeland security or monitoring regional environment. Secondly, near-space provides an optimal solution to relative HRWS SAR imaging. Moreover, as motion compensation is a common technical challenge for the described radars, an active transponder-based motion compensation is also described.
Highlights
Current spaceborne and airborne radars have been playing an important role in remote sensing applications [1, 2, 3]; even as good as they are envisioned and employed, it is impossible to provide a staring presence on a timescale of days, weeks, or months over a selected target or area of interest
To achieve persistent regional remote sensing, we proposed the concept of near-space platform-based passive radar imaging
The signal-to-noise ratio (SNR) is favorable owing to an essentially long integration time. This SNR can be further improved by using non-coherent integration of the signals from more than one receiver channel, weak signal detection and processing is a technical challenge for near-space passive radars
Summary
Current spaceborne and airborne radars have been playing an important role in remote sensing applications [1, 2, 3]; even as good as they are envisioned and employed, it is impossible to provide a staring presence on a timescale of days, weeks, or months over a selected target or area of interest. The requirements of stealth and robust survivability in military applications call for new radar platforms other than satellites and airplanes [5] Those aims can be simultaneously obtained by near-space platforms at a fractional cost of the traditional platforms [6]. Not constrained by orbital mechanics like satellites and high fuel consumption like airplanes, near-space platforms can stay at a specific site for a long time to provide a persistent region coverage. Several near-space vehicle-based microwave remote sensing techniques including passive bistatic radar imaging and high-resolution and wide-swath (HRWS) SAR imaging, along with their potentials and challenges, are investigated in Section 3 and Section 4, respectively. Strict position and altitude information are required to ensure success, but high-precision motion measurement assets widely used in current radar systems may not be reachable for near-space platforms because of its limited load capability.
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