• Current Research on Agriculture and Life Sciences
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• v.31 no.2
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• pp.131-138
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• 2013

The precision aerial application of small farms, such as paddy, upland and orchard fields using agricultural unmanned helicopters became a new paradigm. The objective of this study was to evaluate the performance of a GPS module and algorithm, controlling drift of agricultural helicopter by the crosswind and maintaining the position for emergency landing. Purpose of the drift control, of which an algorithm works while hovering is related with the emergency sequence that coping with abnormal conditions of rotorcraft system. However, the inertial attitude control cannot detect a drifting motion of fuselage moving at the constant velocity, thus the crosswind takes the helicopter away from the landing position. Performance of the drift control module, based on the GPS that a hovering position did not deviate within 5m in diameter, were tested and evaluated. Initially, the reaction against a disturbing gust wind was sensitive, soon the helicopter maintained its locking position and azimuth within 5m in diameter. It was, however, difficult for the helicopter to recognize the swaying and nodding, the some deviation was expected due to the discrepancy characteristics of the GPS signal. The performance of the drift control proved the effectiveness of the module to maintain the position against an unintended drift during the emergency landing or hovering.

• Korean Journal of Remote Sensing
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• v.34 no.6_4
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• pp.1489-1501
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• 2018

In 2016 Kumamoto, Japan, the foreshocks of $M_j$ 6.5 and 6.4, mainshock of $M_j$ 7.3 besides more than 2,000 aftershocks occurred in succession. Large surface deformation occurred due to this serial earthquakes and three-dimensional measurements of the deformation have been presented for the study of fault structures (Baek, 2017). The 3d measurements retrieved from two ascending pairs (20160211_20160602, 20151119_20160616) and a descending pair (20160307_20160418) acquired from ALOS PALSAR-2. In order to avoid mixing ionospheric error components on along-track surface deformation, the descending multiple-aperture interferogram, which do not contain the deformation of aftershocks after 20160418, was utilized. For these reason, there was a temporal discrepancy of about 2 months in extracting the north-south deformation. In this study, we applied a directional filter based ionospheric correction to ascending multiple-aperture interferograms, in order to reduce this discrepancy and understand more accurate fault movements. As a result of the ionospheric correction, an additional displacement signal was observed nearby fault lines. The root-mean-squared errors compared to GPS were about 9.87, 8.13 cm respectively. These results show improvements of 4.8 and 6.4 times after ionospheric correction. We expected that these along-track measurements would be used to decide more accurate movements of faults related to the 2016 Kumamoto Earthquake.