DSpace Collection:

High-resolution hyperspectral imagery from pushbroom scanners on unmanned aerial systems

2022-08-01T00:00:00Z

Title: High-resolution hyperspectral imagery from pushbroom scanners on unmanned aerial systems Authors: Kim, Jae-In; Chi, Junhwa; Ali Masjedi; John Evan Flatt; Melba M. Crawford; Ayman F. Habib; Lee, Joohan; Kim, Hyun-cheol Abstract: Hyperspectral data are gaining popularity in remote sensing and signal processing communities because of the increased spectral information relative to multispectral data. Several airborne and spaceborne hyperspectral datasets are publicly available, facilitating the development of various applications and algorithms. However, hyperspectral data are usually limited by their narrow, highly correlated, and contiguous spectral bands in both processing and analysis. Moreover, the resolution of available hyperspectral datasets is not sufficiently high for the identification of small objects. Nevertheless, with the rapidly advancing technology, hyperspectral imaging systems can now be mounted on small aerial vehicles for detecting small objects at low altitude. To properly handle these high spectral and spatial resolution data, new or redesigned data processing or analysis pipelines must be developed, but such datasets are limited. In this study, we describe two hyperspectral datasets acquired by a drone and evaluate their radiometric and geometric quality. Based on appropriate data acquisition and processing approaches, our datasets are expected to be useful as testbeds for new algorithms and applications.

Design of an Absorptive High-Power PIN Diode Switch for an Ultra-Wideband Radar

2022-04-01T00:00:00Z

Title: Design of an Absorptive High-Power PIN Diode Switch for an Ultra-Wideband Radar Authors: ELLURU, DEEPAK N.; AWASTHI, ABHISHEK K.; GOGINENI, S. PRASAD; TAYLOR, DREW; SHAHABI, ALI; LEMMON, ANDREW N.; CHUNG, CHANGHYUN; LEE, JOOHAN Abstract: This paper details the development of a low-loss, PIN diode single-pole double-throw (SPDT) absorptive switch for an ultra-wideband radar. The fabricated switch operates with a peak power of 200 watts at a 10% duty cycle. It has an insertion loss of less than 0.8 dB, a return loss greater than 19 dB, and isolates the transmitter and receiver beyond 37 dB over the frequency band (170 MHz-470MHz) for sensitive radar measurements. An external RF limiter and a low-power CMOS switch at the receiving end are used to reduce video leakage from the PIN diode switch and enhance the isolation up to 80 dB. A fast-switching MOSFET-based PIN diode driver circuit is designed with a dead-time control circuit to minimize the cross-conduction currents for the PIN diode switch. The rise and fall times for the PIN diode switch are less than 200 ns. The switch-driver includes integrated low-noise power supplies that generate -50 V, 15 V, and 5 V from a common rail 50 V input source.

Time-lapse electrical resistivity tomography and ground penetrating radar mapping of the active layer of permafrost across a snow fence in Cambridge Bay, Nunavut Territory, Canada: correlation interpretation using vegetation and meteorological data

2021-12-01T00:00:00Z

Title: Time-lapse electrical resistivity tomography and ground penetrating radar mapping of the active layer of permafrost across a snow fence in Cambridge Bay, Nunavut Territory, Canada: correlation interpretation using vegetation and meteorological data Authors: Kim, KwanSoo; Lee, Joohan; Ju, Hyeontae; Jung, Ji Young; Chae, Namyi; Chi, Junhwa; Kwon, Min Jung; Lee, Bang Yong; Wagner, Johann; Kim, Ji-Soo Abstract: The active layer thickness (ALT) is a key parameter for permafrost studies. Changes in the ALT are affected mainly by air and ground temperatures, physical and thermal properties of the surface and subsurface materials, soil moisture, vegetation, and the duration and thickness of snow cover. Ground penetrating radar (GPR) and electrical resistivity tomography (ERT) were employed across a snow fence during the thawing season to delineate and monitor the active layer of permafrost in Cambridge Bay, Nunavut, Canada. The variation of the ALT is well captured by the high-resolution time-lapse radargram. At the position of the fence, the active layer thickens over the thawing period from 0.5 m depth at the beginning to 1.0 m depth at the end. The active layer is thicker in the pre-fence area (C zone) than in the post-fence area (H zone). As the air temperature increases with time, the difference in thickness between the two zones decreases, eventually becoming almost equal. Changes in the ALT are represented in the ERT by low resistivities (< 200 omega m), which decrease gradually with time. This occurs most significantly in the H zone due to the rapidly increasing temperature in the absence of snow cover. The electrical resistivity structure of the active layer is well correlated with the vegetation activity, as measured by the normalized difference vegetation index, air/ground temperatures, soil moisture, snow cover, and snow accumulation controlled by the fence. Geophysical data interpretation and correlation schemes with vegetation and meteorological data explored in this paper can be applied to monitor the active layer, which is expected to thin during the freezing season.

Ground Penetrating Radar Imaging of a Circular Patterned Ground near King Sejong Station, Antarctica

2021-09-01T00:00:00Z

Title: Ground Penetrating Radar Imaging of a Circular Patterned Ground near King Sejong Station, Antarctica Authors: Kim, KwanSoo; Ju, Hyeontae; Lee, Joohan; Chung, Changhyun; Kim, Hyoungkwon; Lee, Sunjoong; Kim, Jisoo Abstract: Constraints on the structure and composition of the active layer are important for understanding permafrost evolution. Soil convection owing to repeated moisture-induced freeze-thaw cycles within the active layer promotes the formation of self-organized patterned ground. Here we present the results of ground penetrating radar (GPR) surveys across a selected sorted circle near King Sejong Station, Antarctica, to better delineate the active layer and its relation to the observed patterned ground structure. We acquire GPR data in both bistatic mode (common mid-points) for precise velocity constraints and monostatic mode (common-offset) for subsurface imaging. Reflections are derived from the active layer-permafrost boundary, organic layer-weathered soil boundary within the active layer, and frozen rock-fracture-filled ice boundary within the permafrost. The base of the imaged sorted circle possesses a convex-down shape in the central silty zone, which is typical for the pattern associated with convection-like soil motion within the active layer. The boundary between the central fine-silty domain and coarse-grained stone border is effectively identified in a radar amplitude contour at the assumed active layer depth, and is further examined in the frequency spectra of the near- and far-offset traces. The far-offset traces and the traces from the lower frequency components dominant on the far-offset traces would be associated with rapid absorption of higher frequency radiowave due to the voids in gravel-rich zone. The presented correlation strategies for analyzing very shallow, thin-layered GPR reflection data can potentially be applied to the various types of patterned ground, particularly for acquiring time-lapse imaging, when electric resistivity tomography is incorporated into the analysis.