• Journal of the Institute of Electronics Engineers of Korea SP
• /
• v.40 no.1
• /
• pp.130-138
• /
• 2003

The classical image reconstruction for stripmap-mode Synthetic Aperture Radar is the Range-Doppler algorithm. When the spotlight-mode SAR system was envisioned, Range-Doppler algorithm turned out to fail rapidly in this SAR imaging modality. Thus, what is referred to as Polar format algorithm, which is based on the Plane wave approximation, was introduced for imaging from spotlight-mode SAR raw- data. In this paper, we have studied for the raw data processing schemes in the spotlight-mode Synthetic Aperture Radar. We apply the Wavefront Reconstruction scheme that does not utilize the approximation in spotlight-mode SAR imaging modelity, and compare the performance of target imaging with the Polar format inversion scheme.

• Proceedings of the IEEK Conference
• /
• 2000.11a
• /
• pp.501-504
• /
• 2000

The classical image reconstruction for stripmap SAR is the range-Doppler imaging. However, when the spotlight SAR system was envisioned, range-Bowler imaging fumed out to fail rapidly in this SAR imaging modality. What is referred to as polar format processing, which is based on the plane wave approximation, was introduced for imaging from spotlight SAR data. This paper has been studied for the raw data processing schemes in the spotlight-mode synthetic aperture radar. we apply the wavefront reconstruction scheme that does not utilize the approximation in spotlight-mode SAR imaging modelity, and compare the performance of target imaging with the polar format inversion scheme.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.39 no.2
• /
• pp.183-194
• /
• 2011

Synthetic aperture radar (SAR) is widely used because of high resolution imaging capability in all weather and day/night condition. In this paper development of Spotlight SAR simulator is proposed for image quality analysis. Proposed SAR simulator is based on the SAR system design parameters so that SAR image performance can be expected which is essential throughout the full system development procedure from the initial concept design stage to the final in-flight calibration and validation stage. The raw data of ideal point target is first generated by taking account of the flight and imaging geometry and the various SAR system design parameters, and the Spotlight image formation algorithm is implemented in order to obtain the point target response. Finally the image quality of the generated raw data is analyzed in terms of spatial resolution, peak to sidelobe ratio and integrated sidelobe ratio.

• 제어로봇시스템학회:학술대회논문집
• /
• 2005.06a
• /
• pp.857-860
• /
• 2005

Several algorithms have been developed for the data processing of spotlight synthetic aperture radar (SAR). In particular, the range migration algorithm (RMA) does not assume that illuminating wavefronts are planar. Also, a high resolution image can be obtained by the RMA. This paper introduces an extension of the original RMA to enable a more efficient airborne SAR data processing. We consider more general motion and scene than the original RMA. The presented formulation is analyzed by using the principle of the stationary phase. Finally, the extended algorithm is tested with numerical simulations using the pulsed spotlight SAR.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.40 no.1
• /
• pp.49-60
• /
• 2012

Synthetic aperture radar (SAR) has been employed in various fields due to its capability to generate high resolution images regardless of weather and visibility. This paper presents a performance analysis on the image formation of high resolution SAR according to various slant range distance and synthetic aperture lengths using a range migration algorithm simulator. Although the visual performance on the SAR image is more accurate, a numeric analysis resulted in a comparable measurement. More specifically, raw data were generated for an ideal point target upon imaging geometries and design parameters such as slant range distance and synthetic aperture lengths. Finally, spatial resolution, peak to sidelobe ratio and integrated sidelobe ratio are drawn to provide SAR capabilities in the initial concept design, final in-flight calibration and validation stages.

• Proceedings of the IEEK Conference
• /
• 2000.11a
• /
• pp.505-508
• /
• 2000

The success of target reconstruction in SAR(Synthetic Aperture Radar) imaging system is greatly dependent on the coherent detection. Primary causes of incoherent detection are uncompensated target or sensor motion, random turbulence in propagation media, wrong path in radar platform, and etc. And these appear as multiplicative phase error to the echoed signal, which consequently, causes fatal degradations such as fading or dislocation of target image. In this paper, we present iterative phase error estimation scheme which uses echoed data in all temporal frequencies. We started with analyzing wave equation for one point target and extend to overall echoed data from the target scene - The two wave equations governing the SAR signal at two temporal frequencies of the radar signal are combined to derive a method to reconstruct the complex phase error function. Eventually, this operation attains phase error correction algorithm from the total received SAR signal. We verify the success of the proposed algorithm by applying it to the simulated spotlight-mode SAR data.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.20 no.2
• /
• pp.183-192
• /
• 2009

SAR(Synthetic Aperture Radar) is an all-weather imaging radar and is widely used in military and civil application. Especially high-resolution SAR images are very important in military purpose because it can be used at target recognition application. LIG Nex1 developed a SAR system called NexSAR with bandwidth of 600 MHz and resolution of 30 cm to obtain technologies required for high-resolution SAR. To achieve 600 MHz bandwidth of waveform generator, two DDSs are used and its output signals are SSB modulated. And deramp technique is used to reduce the sampling rate of ADC at high resolution mode. NexSAR has stripmap and spotlight modes and its functionality and performances are evaluated through ground and flight tests.

• Journal of Korean Society of Industrial and Systems Engineering
• /
• v.45 no.2
• /
• pp.12-19
• /
• 2022

Artificial intelligence is driving the Fourth Industrial Revolution and is in the spotlight as a general-purpose technology. As the data collection from the battlefield increases rapidly, the need to us artificial intelligence is increasing in the military, but it is still in its early stages. In order to identify maritime targets, Republic of Korea navy acquires images by ISAR(Inverse Synthetic Aperture Radar) of maritime patrol aircraft, and humans make out them. The radar image is displayed by synthesizing signals reflected from the target after radiating radar waves. In addition, day/night and all-weather observations are possible. In this study, an artificial intelligence is used to identify maritime targets based on radar images. Data of radar images of 24 maritime targets in Republic of Korea and North Korea acquired by ISAR were pre-processed, and an artificial intelligence algorithm(ResNet-50) was applied. The accuracy of maritime targets identification showed about 99%. Out of the 81 warship types, 75 types took less than 5 seconds, and 6 types took 15 to 163 seconds.

• Korean Journal of Remote Sensing
• /
• v.27 no.2
• /
• pp.151-161
• /
• 2011

PGA(Phase Gradient Autofocus) is a representative autofocus technique to improve the SAR(Synthetic Aperture Radar) image quality. PGA can estimate high order phase errors and have good robustness in noisy environments. However, PGA is not suitable to apply to the stripmap mode data directly because it is based on the spotlight mode operation. In this paper, the PGA implementation technique for stripmap mode data and the method of ROI(Region of Interest) selection that affects severely on PGA performance have been proposed. The proposed technique was verified by the point target simulation first, and was applied to the real SAR signal data acquired by the flight test. Finally, the significant improvements in focusing quality were shown in the processed SAR images using the proposed method.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.44 no.10
• /
• pp.921-932
• /
• 2016

In this paper, a modified FSA(Frequency Scaling Algorithm) is proposed for KOMPSAT-5 high-resolution SAR image generation. In order to enhance performance of azimuth compression, degraded in sub-aperture processing due to the imperfect geometric parameter of data acquisition, the full-aperture signal processing algorithm is designed based on the exact time-frequency analysis. In addition, an azimuth scaling function is newly devised to make the full-aperture processing algorithm suitable for KOMPSAT-5 sliding-spotlight mode. Different from the previous sub-aperture FSA schemes, the suggested technique could accommodate the merit of unified signal processing structure regardless of operational modes of KOMPSAT-5. Through the point target simulation, it is verified that the suggested algorithm provides superior performance of azimuth compression over the existing full-aperture processing methods. The experimental results using real data acquired by KOMPSAT-5 are also given to demonstrate the effectiveness of our scheme as well.