Ultrasonic wave is suitable to be used as information carrier in short-range remote sensing practices. When developing a short-range ultrasonic remote sensing device, the object distance measurement routine shall produce an accurate result. In a few-meter or several-meter object detection or imaging, millimeter accuracy is required, therefore, a calibration becomes crucial. This article addresses the process and the result of our research on calibrating the distance between the device and the backscattering object. Our approach consists of investigating potential delay contributors, recognizing the practical delay contributors by analysing the program routine, formulating the calibration equation and applying the calibration equation in the computation.

In this paper, a soil moisture retrieval from full-polarimetric synthetic aperture radar (SAR) data is investigated for sparsely vegetated soil surfaces. An improved retrieval method adapting the variations in vegetation is proposed by incorporating the generalized volume model into the polarimetric two-scale two-component model (PTSTCM). The feasibility of the method, termed as the adaptive PTSTCM, has been tested for tropical peatland sites in Indonesia which exhibit a variety of sparse vegetation cover on soil after land clearing activities. The data were collected in March and August 2017 with the time domain reflectometry (TDR) probe for a total of 18 sample points over 11 regions. The method was applied to ALOS-2 L-band quad-pol SAR data that were acquired simultaneously with field measurements. We compared the results between the proposed adaptive PTSTCM and the original PTSTCM that utilizes specific types of volume model (i.e., randomly, horizontally, and vertically oriented volume models). Scatterplots of estimated versus measured results reveal that the adaptive PTSTCM yields a root-mean-square error (RMSE) of 5.1vol. and inversion rate of 35.0 and 58.5 for March and August data, respectively, which are found to be superior to those of the original PTSTCM.

This paper aims to present the design and development work of a full polarimetric Circularly Polarized Synthetic Aperture Radar (CP-SAR) system. The CP-SAR sensor is operating in C band with center frequency of 5.3 GHz, operational bandwidth ranged from 100 MHz to 400 MHz, and transmitting peak power of 280 watt. Four circularly polarized antennas (2 units with left handed circularly polarized and 2 units with right handed circularly polarized) were designed and developed with approximately 22 dBic of gain, and beamwidth of 13° and 6° in range and azimuth direction, respectively. This paper also presents the results from the laboratory test and ground test of the CP-SAR sensor, as well as, the flight test results obtained from the maiden flight of the CP-SAR system using CASA/IPTN CN235-MPA aircraft.

This paper presents the development work of a PC-based airborne SAR baseband system that integrates commercial off-the-shelf Arbitrary Waveform Generator (AWG) and high-speed digitizer, and a custom-designed Timing and Control Unit (TCU). The proposed system is general purpose, in which the critical operating parameters such as waveform modulation format, baseband bandwidth, pulse width, pulse repetition frequency, and all the relevant timing and control signals are re-configurable in real-time. As a brief functional summary of the system, it can, i) generates 2-channel (I & Q) of 1.2 GHz (maximum) bandwidth chirp signal with its pulse width ranged from 0.5 us to 100 mu s, ii) able to digitize 2-channel (I & Q) of 1 GHz (maximum) bandwidth chirp echoes with on-board 4 G-Samples of recording buffer, and iii) generate accurate and precise timing and control signals with timing resolution of 10 ns. The system is currently deployed as the baseband and control system for Josaphat Microwave Remote Sensing Laboratory (JMRSL) C band airborne full polarimetric Circularly Polarized Synthetic Aperture Radar (CP-SAR) sensor built for Earth surface, environmental, and disaster monitoring.

Despite the long history and wide application of computer simulation on wave propagation, it is found interesting that study on numerical solution to estimate the amount of received power at the receiving antenna is limited. While, in preparing a radio transmission system, including a SAR system, the estimation of received power is crucial. A good estimation on received power shall reduce the probability of an on-field failure. This article is mainly aimed to addresses several aspects in concepting the solution to this issue. In particular, a ground-based C-band SAR test scenario using a 5.3 GHz carrier and our newly designed transmitting and receiving antennas has been taken as a case as the simulation model.