Raw Data Simulation of Spaceborne Synthetic Aperture Radar with Accurate Range Model

Abstract

Simulated raw data have become an essential tool for testing and assessing system parameters and imaging performance due to the high cost and limited availability of real raw data from spaceborne synthetic aperture radar (SAR). However, with increasing resolution and higher orbit altitudes, existing simulation methods fail to generate SAR simulated raw data that closely resemble real raw data. This is due to approximations such as curved orbits, “stop-and-go” assumption, and Earth’s rotation, among other factors. To overcome these challenges, this paper presents an accurate range model with a “nonstop-and-go” configuration for raw data simulation based on existing time-domain simulation methods. We model the SAR echo signal and establish a precise space geometry for spaceborne SAR. Additionally, we precisely identify the target illumination area based on elliptical beams through space coordinate transformation. Finally, the SAR raw data were accurately simulated using high-precision time-domain simulation methods. The accuracy of the proposed model was validated by comparing it with the traditional hyperbolic model and the curved orbit model with “stop-and-go” assumption through image processing of the generated raw data. Through the analysis of point target quality parameters, the errors of various parameters in our distance model compared with the other two models are within 1%. Furthermore, this simulation method can be adapted to simulate raw data of other modes and satellite orbits by adjusting beam control and satellite orbit parameters, respectively. The proposed simulation method demonstrated high accuracy and versatility, thereby providing a valuable contribution to the development of remote sensing technology.

Accurate Range Modeling for High-Resolution Spaceborne Synthetic Aperture Radar

“…The radar adjusts the antenna beam to ensure continuous target illumination during the synthetic aperture time T a . However, as the resolution increases, T a also increases, and the actual trajectory of the radar cannot be accurately represented as a straight-line motion at a constant velocity v [32], leading to defocusing effects in SAR data processing. The radar transmits a linear frequency modulation (LFM) signal in the range direction, and the received signal is obtained after propagating through the two-way range.…”

“…where A 0 is a complex constant, τ and η represent the range and azimuth time, respectively, η c denotes the center moment of the synthetic aperture time, w r (•) and w a (•) are the range and azimuth envelopes, c is the speed of light, λ is the radar carrier wavelength, and K r is the FM rate of the transmitted pulse chirp [32].…”

“…The primary influence on a satellite's orbit around the Earth is the gravitational interaction between the satellite and the Earth itself. Thus, a simplified two-body orbit model suffices to characterize the satellite's trajectory [32][33][34]. Figure 3 depicts the spatial geometry of spaceborne SAR within the Earth-centered inertial coordinate system (ECI) [32].…”

“…Thus, a simplified two-body orbit model suffices to characterize the satellite's trajectory [32][33][34]. Figure 3 depicts the spatial geometry of spaceborne SAR within the Earth-centered inertial coordinate system (ECI) [32]. The satellite's position along its elliptical orbit is defined by six orbital elements: the semi-major axis a, eccentricity e, inclination i, right ascension of the ascending node (RAAN) Ω, argument of perigee ω, and true anomaly f [32,34].…”

“…In the absence of external perturbation forces, Kepler's three laws can be employed to compute the satellite's orbit. The equation describing the satellite's orbit [32,33] is…”