A High-Resolution SAR Focusing Experiment Based on GF-3 Staring Data

Abstract

Spotlight synthetic aperture radar (SAR) is a proven technique, which can provide high-resolution images as compared to those produced by traditional stripmap SAR. This paper addresses a high-resolution SAR focusing experiment based on Gaofen-3 satellite (GF-3) staring data with about 55 cm azimuth resolution and 240 MHz range bandwidth. In staring spotlight (ST) mode, the antenna always illuminates the same scene on the ground, which can extend the synthetic aperture. Based on a two-step processing algorithm, some special aspects such as curved-orbit model error correction, stop-and-go correction, and antenna pattern demodulation must be considered in image focusing. We provide detailed descriptions of all these aspects and put forward corresponding solutions. Using these suggested methods directly in an imaging module without any modification for other data processing software can make the most of the existing ground data processor. Finally, actual data acquired in GF-3 ST mode is used to validate these methodologies, and a well-focused, high-resolution image is obtained as a result of this focusing experiment.

Channel Imbalances and Along-Track Baseline Estimation for the GF-3 Azimuth Multichannel Mode

“…Gaofen-3 (GF-3) is a Chinese C-band spaceborne SAR which was launched in August 2016, in Taiyuan (Shanxi Province, China), and then went through a four-month payload performance commission phase and a two-month application performance commission phase [15,16]. Since January 2017, GF-3 has provided customers with advanced, commercially-available spaceborne SAR products which have fully polarization mode, and the azimuth resolution can be as fine as 0.55 m in a staring spotlight experiment [17]. GF-3 is the first Chinese spaceborne AMC SAR which contains two receiving apertures along the azimuth, and has acquired more than 20,000 images in ultrafine stripmap (UFS) mode, i.e., the dual-receive stripmap mode described in [15].…”

Processing of Very High Resolution GF-3 SAR Spotlight Data With Non-Start–Stop Model and Correction of Curved Orbit

“…3. This effect will introduce a range-azimuth coupling phase term in 2-D-frequency domain [14], [38].…”

“…GF-3 not only plays an important role in the fields of marine environment monitoring, resource investigation, disaster prevention, and water conservancy but also provides high-quality data for scientific experiments [11]. In order to exploit the maximum azimuth steering capability of the GF-3 SAR system, spotlight experiments were performed after the satellite had been in operational mode [14].…”

“…The GF-3 data experiment also demonstrates the feasibility of the proposed method. The antenna pattern, topography dependence, and atmospheric effects, which should be considered in very high-resolution spaceborne SAR, have been systematically discussed in [14], [16], and [37], thus, they are not explained in detail in the article.…”

An Accurate Measurement Method for Azimuth Pointing of Spaceborne Synthetic Aperture Radar Antenna Beams Based on Ground Receiver

“…The satellite speed measurement error is within 1m/s, the precision track data can reach 0.1 m/s [ 18 , 19 , 20 ]; after the slant range calibration, the accuracy of the slant range can reach 1 m [ 21 , 22 ]. Since the orbital altitude of LEO SAR satellites is generally in the range of 500 km to 800 km [ 23 ], and the speed is approximately 7500 m/s [ 24 ], the ratio of satellite speed measurement error and the ratio of slant range measurement error is very small, and the resulting error can be ignored.…”