Jyunpei Uemoto

Calibration experiments of advanced X-band airborne SAR system, Pi-SAR2

In the National Institute of Information and Communications Technology, Japan (NICT), we have developed an advanced X-band airborne synthetic aperture radar (SAR) system, Pi-SAR2, since 2006, to succeed the X-band polarimetirc and interferometric airborne SAR, Pi-SAR. The Pi-SAR2 has a higher spatial resolution of 0.3–0.6 m in the azimuth direction and 0.3–0.5 m in the range direction, as well as polarimetric and interferometric observation functions. The calibration experiments of the Pi-SAR2 were carried out as a part its test flights in December 2008 and February 2010. Calibration targets were deployed on a runway of the Taiki Aerospace Experiment Field in Hokkaido, Japan, to be observed.

Low‐latitude ionospheric height variation as observed by meridional ionosonde chain: Formation of ionospheric ceiling over the magnetic equator

A multipoint ionosonde observation campaign was conducted along the magnetic meridional plane in Southeast Asia to study ionosphere-thermosphere coupling. One station was near the magnetic equator and two of the other stations were at off-equatorial latitudes (∼10° magnetic latitude). The daytime ionospheric peak height (hmF2) was analyzed for each season during the solar minimum years, 2006–2007 and 2009. The peak height increased for ∼3 h after sunrise at the magnetic equator and off-equatorial latitudes, as expected from the daytime upward E × B drift. The apparent upward drift at the magnetic equator ceased before noon, while the drift at the off-equatorial latitudes continued upward and the layer height exceeded the equatorial height around noon. The noontime limited layer peak height at the magnetic equator, which was termed the ionospheric ceiling, did not depend on the season, while the maximum peak height at the off-equatorial latitudes largely varied with each season. Numerical modeling using the SAMI2 code was conducted and the features of the ionospheric ceiling were reproduced quite well. The dynamical parameters provided by the SAMI2 modeling runs showed that the ionospheric ceiling is formed by the field-aligned plasma diffusion, which is a part of the fountain effect.

Performance evaluation on cross-track interferometric SAR function of the airborne SAR system (PI-SAR2) OF NICT

The National Institute of Information and Communications Technology (NICT) developed an airborne X-band SAR system (Pi-SAR2: polarimetric and interferometric SAR 2) to monitor the earths environment and disasters [1]. Pi-SAR2 has polarimetric and interferometric functions with high spatial resolution of 0.3m [2]. In this paper we describe the single-pass interferometric function of Pi-SAR2 and show the performance evaluation on the interferometric function of Pi-SAR2 by using corner reflectors. Moreover we describe the volcanic monitoring by using interferometric SAR.

Development of the onboard processor for Pi-SAR2

The synthetic aperture radar (SAR) has been utilized for monitoring natural disaster areas because the SAR observation can be performed irrespective of the daylight and weather conditions. To reduce the time from observation to distributing SAR images to the headquarters for disaster control and disaster area, we have developed an onboard processor which is capable of doing a full-spec processing for the airborne SAR called as the polarimetric and interferometric SAR (Pi-SAR2) since 2009. We demonstrated that the developed onboard processor is effective to reduce the time from observation to distribution and the SAR image can be transferred to the ground within 15 min after observation via the communication satellite called as the engineering test satellite VIII (ETS-VIII) in the experiments on March 2011.

Damage estimation of the Great East Japan earthquake with airborne SAR (PI-SAR2) data

A 9.0-magnitude earthquake occurred off the pacific coast of Tohoku area of Japan, in March 2011. Accompanied with the subsequent tsunami, it caused a lot of casualties and damages in the coast area. We conducted urgent observations of the damaged areas with an airborne X-band SAR system, Pi-SAR2, immediately after the earthquake, on March 12 and the following dates. The Pi-SAR2 is a fully polarimetric airborne radar, with high spatial resolution of 0.3 m. We found the high resolution radar images, with multi-temporal observations, are quite useful to estimate the area flooded by the tsunami and its changes. Also found is capability of the polarimetric radar images to estimate the amount of a pile of debris that is one of the greatest concerns for the residents.

Evaluation of digital elevation model generated by an airborne interferometric SAR (Pi-SAR2)

This paper addresses the evaluation of the digital elevation model (DEM) generated by single pass SAR interferometry using an X-band airborne SAR (Pi-SAR2). In this paper we describe the evaluation experiments by using corner reflectors and show the result of the height accuracy on DEM by the cross-track interferometric function of Pi-SAR2.

Preliminary analysis of cross-track interferometry by synthetic beam of two antennas of along-track interferometric SAR

Many parameters are required for the measurement of the sea surface currents and the sea levels simultaneously by the along-track interferometry SAR (AT-InSAR). To estimate the elevation or the sea levels from the signals observed by the AT-InSAR, the method for synthesizing these received signals was developed. To evaluate the estimation method, the ground surface was observed by the cross-track interferometrie SAR (CT-InSAR) and AT-InSAR. In addition, to clarify the accuracy of the digital surface model (DSM) estimated from the signals observed by the AT-InSAR, The experiment with the corner reflectors was conducted. As a result, it became clear that the DSM can be estimated from the signals observed by the AT-InSAR.

Development of Pi-SAR2 along-track interferometric SAR system

To detect the moving targets such as cars or ships, we developed along-tack interferometric SAR (AT-InSAR) system and added its function on NICT airborne SAR. Our AT-InSAR can measure the moving targets in the single (VV) and dual (VV and VH) polarization. The dual polarization mode has more degree of freedom compared to the single polarization mode. The preliminary experiment for verifying its performance carried out on the farm road. First of all, to arrange the triangular and square trihedral corner reflectors in the azimuth direction, we checked and confirmed the performance of AT-InSAR antenna. Then, we checked its ability to indicate the moving target by observing the truck running toward the range direction at a constant velocity. Finally, we verified the accuracy of its velocity estimated from AT-InSAR data and clarified that its velocity was estimated from VV AT-InSAR data highly accurately.

Damage detection of the great east Japan earthquake by the airborne SAR (PI-SAR2) of NICT

The great east Japan damaged the east coast of Japan severely. NICT conducted urgent observations of the damaged areas by an airborne X-band SAR system (Pi-SAR2: polarimetric and interferometric SAR 2). In this paper we describe the detection of the damaged area by the earthquake and tsunami with polarimetric SAR data of Pi-SAR2. The space resolution of Pi-SAR2 is 0.3 m (slant-range) [1][2]. These SAR images of Pi-SAR2 are useful to detect the destruction of buildings and bridges and to identify flooded areas from the viewpoint of high resolution. We continue to observe the damaged area by Pi-SAR2 to monitor the reconstruction.

Landslide detection based on height and amplitude differences using pre- and post-event airborne X-band SAR data

The recognition of landslides and making their inventory map are considered to be urgent tasks not only for damage estimation but also for planning rescue and restoration activities. Owing to the capability of synthetic aperture radar (SAR) for day-and-night and all-weather imaging, various studies utilizing SAR data for landslide detection have been reported to date. Among the detection methods utilizing SAR data, those based on height differences accompanying landslides are attractive and should be further improved, since they can directly contribute to damage estimation through a volumetric estimation of landslides. In this context, we propose in this paper a landslide detection method utilizing height differences derived from pre- and post-event SAR digital elevation models (DEMs) combined with amplitude differences. The proposed method was applied to the landslides triggered by the 2016 Kumamoto earthquake. The application results demonstrate that SAR DEMs with a high altitudinal resolution can improve the detection ability and that the incorporation of the amplitude differences is effective for decreasing the number of false detections. Although the reliability of the proposed method is deemed moderate when evaluated on the basis of the kappa coefficients derived through an accuracy assessment, most of the outliers are correctly filtered out and large- and medium-scale landslides are detected. Therefore, the inventory maps derived from the proposed method are thought to be effective at the initial stage of planning rescue and restoration activities.