Vegetation water content (VWC) is an important biophysical parameter and has a significant role in the retrieval of soil moisture using microwave remote sensing. Here, the radar vegetation index (RVI) was evaluated for estimating VWC. Analysis utilized a data set obtained by a ground-based multifrequency polarimetric scatterometer system, with a single incidence angle of 40^°, during an entire growth period of rice and soybean. Temporal variations of the backscattering coefficients for the L-, C-, and X-bands, RVI, VWC, leaf area index, and normalized difference vegetation index were analyzed. The L-band RVI was found to be correlated to the different vegetation indices. Prediction equations for the estimation of VWC from the RVI were developed. The results indicated that it was possible to estimate VWC with an accuracy of 0.21 kg·m^-2 using L-band RVI observations. These results demonstrate that valuable new information can be extracted from current and future radar satellite systems on the vegetation condition of two globally important crop types. The results are directly applicable to systems such as the proposed NASA Soil Moisture Active Passive satellite.

Lake ice is a robust indicator of climate change. The availability of information contained in Moderate Resolution Imaging Spectroradiometer (MODIS) daily snow products from 2000 to 2017 could be greatly improved after cloud removal by gap filling. Thresholds based on open water pixel numbers are used to extract the freeze‐up start and break‐up end dates for 58 lakes on the Tibetan Plateau (TP), 18 lakes are also selected to extract the freeze‐up end and break‐up start dates. The lake ice durations are further calculated based on freeze‐up and break‐up dates. Lakes on the TP begin to freeze‐up in late October and all the lakes start the ice cover period in mid‐January of the following year. In late March, some lakes begin to break‐up, and all the lakes end the ice cover period in early July. Generally, the lakes in the northern Inner‐TP have earlier freeze‐up dates and later break‐up dates (i.e. longer ice cover durations) than those in the southern Inner‐TP. Over 17 years, the mean ice cover duration of 58 lakes is 157.78 days, 18 (31%) lakes have a mean extending rate of 1.11 d yr^‐1 and 40 (69%) lakes have a mean shortening rate of 0.80 d yr^‐1. Geographical location and climate conditions determine the spatial heterogeneity of the lake ice phenology, especially the ones of break‐up dates, while the physico‐chemical characteristics mainly affect the freeze‐up dates of the lake ice in this study. Ice cover duration is affected by both climatic and lake specific physico‐chemical factors, which can reflect the climatic and environmental change for lakes on the TP.

This paper presents the development of a ground-based arc-scanning synthetic aperture radar (ArcSAR) system mounted on a truck. ArcSAR formulates synthetic aperture by a horizontal circular motion of antennas attached at the end of an extendable boom. The ArcSAR system is designed to operate in two different imaging modes: the spot mode and the scan mode . The spot mode obtains a high-resolution image by fixing the view angle of antennas toward a target. The scan mode obtains wider image coverage with a reduced resolution by fixing the antennas relative to the boom. Different SAR focusing algorithms were implemented for the accuracy and efficiency of image processing: the time domain algorithm for the spot mode and the range Doppler algorithm for the scan mode. An exemplary X-band ArcSAR spot mode image, obtained with a 180 ° scanning of 4-m boom, has an azimuth resolution of 0.07 ° , which is equivalent to the 12.6-m linear scanning of a conventional ground-based SAR system. An ArcSAR scan mode image was successfully obtained as well, covering a 350 ° image area at an azimuth resolution of 1.07 °, which is 11 times better than that of arc-scanning real aperture radar that would have 11.84 ° azimuth resolution.

In November 2017, an $Mw$ 5.4 earthquake with a shallow (⁠$∼4km$⁠) hypocenter occurred in the Pohang area, one of the most developing industrial cities in South Korea. This shock resulted in the costliest earthquake damages in modern Korean history. Immediately after the event, it was not easy to recognize the source fault due to the lack of clear coseismic surface ruptures but also the absence of previously mapped active faults around the epicenter. Based on satellite‐ and unmanned aerial vehicle (UAV)‐derived images, with ground resolution higher than 0.5 m, and field observations, we investigate surface deformation such as sand blows and ground failures associated with the Pohang earthquake as well as bedrock fault exposures in the epicentral area. To better constrain the source fault and deformation mechanism, we combine both moment tensors with aftershock relocations and surface displacements estimated by Interferometric Synthetic Aperture Radar (InSAR). Our results indicate that (1) various types and distributions of secondary ground deformation were controlled by blind oblique‐slip rupture; characterized by right‐lateral and reverse‐slip components, on a reactivated pre‐existing segmented normal‐fault system, and (2) local ground conditions could trigger or amplify ground deformations and their related earthquake damage. Our study highlights the importance of mapping the extent of coseismic deformation as well as the trace of active faults on improving seismic hazard assessments in the Korean Peninsula.

An $Mw$ 5.4 earthquake occurred in the city of Pohang in the southeastern part of the Korean Peninsula on 15 November 2017. It was a moderate‐sized crustal event but triggered enormous attention from the Korean public because strong shaking was felt over the whole country, and it had been just a year since the $Mw$ 5.5 Gyeongju earthquake, the largest instrumentally recorded event in the country. Both earthquakes occurred within 40 km of each other. The Pohang earthquake provides a unique opportunity to constrain the static slip model of an earthquake in Korea using spaceborne Interferometric Synthetic Aperture Radar (InSAR) observations because the focal depth is relatively shallow (⁠$∼4km$⁠), and surface displacement fields were successfully obtained by both descending and ascending orbits of the Sentinel‐1A/B satellites. We performed a linear slip inversion using the InSAR data. Our slip model reveals that a major slip associated with the event occurred in the northeastern part of the hypocenter rather than in the southwestern part. In addition, its rupture dimension and mean slip are 5 km (width) by 6 km (length) and 15 cm, respectively. The InSAR data also show that no significant postseismic deformation occurred after the event.