Electric-field-penetration events have been identified using F-region vertical-drift measurements obtained in the October 6-13, 1984 period by the Jicamarcan incoherent-backscatter radar and corresponding h-prime F measurements from ionosondes at Fortaleza, Cachoeira Paulista, and Dakar. Predictions made using the Rice Convection Model for the pattern, strength, and duration of the low-latitude electric field occurring in response to an increasing high-latitude convection agree with observations. The observed 1-2 h duration of the low-latitude response to decreased convection can be explained by the fossil-wind theory of Richmond (1983).

Penetration of high latitude electric fields effects tolow latitude during Sundial 1984

Differential GPS와 응용

Using machine learning models, remote sensing, and GIS to investigate the effects of changing climates and land uses on flood probability

Flooding is a natural disaster that causes considerable damage to different sectors and severely affects economic and social activities. The city of Saqqez in Iran is susceptible to flooding due to...

Flood susceptibility mapping using an improved analytic network process with statistical models

This study aims to identify the vulnerable landscape areas using landslide frequency ratio and land-use change associated soil erosion hazard by employing geo-informatics techniques and the revised universal soil loss equation (RUSLE) model. Required datasets were collected from multiple sources, such as multi-temporal Landsat images, soil data, rainfall data, land-use land-cover (LULC) maps, topographic maps, and details of the past landslide incidents. Landsat satellite images from 2000, 2010, and 2019 were used to assess the land-use change. Geospatial input data on rainfall, soil type, terrain characteristics, and land cover were employed for soil erosion hazard classification and mapping. Landscape vulnerability was examined on the basis of land-use change, erosion hazard class, and landslide frequency ratio. Then the erodible hazard areas were identified and prioritized at the scale of river distribution zones. The image analysis of Sabaragamuwa Province in Sri Lanka from 2000 to 2019 indicates a significant increase in cropping areas (17.96%) and urban areas (3.07%), whereas less dense forest and dense forest coverage are significantly reduced (14.18% and 6.46%, respectively). The average annual soil erosion rate increased from 14.56 to 15.53 t/ha/year from year 2000 to 2019. The highest landslide frequency ratios are found in the less dense forest area and cropping area, and were identified as more prone to future landslides. The river distribution zones Athtanagalu Oya (A-2), Kalani River-south (A-3), and Kalani River- north (A-9), were identified as immediate priority areas for soil conservation.

Assessing Soil Erosion Hazards Using Land-Use Change and Landslide Frequency Ratio Method: A Case Study of Sabaragamuwa Province, Sri Lanka

Colombo district has become an increasingly congested urban society. It has been reported that the frequent flooding in the Colombo district occurs due to the shrinking of open spaces, illegal constructions, and lack of suitable waste disposal facilities. Therefore, this study focuses on analyzing the impact of land-use change on the flood of Colombo district in May 2016 in comparison to the land-use during the flood in 1989. Accordingly, Landsat images were utilized to identify the land-use by using NDVI, NDBI, and NDWI indices. Out of the several techniques examined, SVM classification was chosen, and change detection techniques in conjunction with remote sensing and GIS environment were adopted. SVM classification showed the highest accuracy for land-use classification, which was 99.0% in 1989 and 99.9% in 2016. The comparison of land-use changes of 1989 and 2016 with similar flood extent of the Colombo district proved that the area of the Kelani river watershed changed into urban area, having a significant impact on flood inundation. The Kelani river watershed includes 23% of the total urban area of the Colombo district. Similarly, the entire area of land-use transformation covered 37.7% of the area within the watershed region of the Colombo district. Eventually, this research identified the significant impact of Colombo district floods in May 2016 on land-use changes.

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Land-Use Change and Its Impact on Urban Flooding: A Case Study on Colombo District Flood on May 2016

Ionospheric total electron content response to September-2017 geomagnetic storm and December-2019 annular solar eclipse over Sri Lankan region

Satellite-Based Augmentation Systems (SBAS) are being developed worldwide due to their unique advantage of wide area coverage. GPS Aided Geo Augmented Navigation (GAGAN) is an Indian implementation of SBAS, with three (03) geo stationary satellites in space covering a huge area even beyond Indian Territory. This study focused on analyzing the improvement in position solution with GAGAN corrections over Sri Lanka. In order to test its performances, several dual and single frequency GNSS receivers were used in this experiment, one receiver was configured as SBAS receiver and other two were kept as GPS stand-alone receivers. Observations were carried out over seven (07) known control stations of six (6) different districts to investigate its coverage over Sri Lanka. At each of the tested stations the GAGAN active L1 receiver has always shown a significant accuracy improvement over L1 uncorrected observations. Further, five out of the seven (7) observation locations the calculated average 3D positional errors were lower than 1m. Almost 79% of observations (out of 24 hours of observations) have shown acceptable 3D positional accuracy, of less than 1m, for many spatial data collection applications. However, the local DGPS correction has shown higher reliability than GAGAN corrections with almost 85% of observations with less than 1m, 3D positional error.

Performance Analysis of GPS Aided Geo Augmented Navigation (GAGAN) Over Sri Lanka

. Through the recent technological developments of radar
and optical remote sensing in (i) the areas of temporal, spectral, spatial,
and global coverage; (ii) the availability of such images either at a low
cost or free of charge; and (iii) the advancement of tools developed in
image analysis techniques and GIS for spatial data analysis, there is a vast
potential for landslide studies using remote sensing and GIS as tools.
Hence, this study aimed to assess the efficacy of using radar-derived factors (RDFs) in identifying landslide susceptibility using the bivariate
information value method (InfoVal method) and the multivariate multi-criteria
decision analysis based on the analytic hierarchy process statistical analysis.
Using identified landslide causative factors, four landslide prediction
models – bivariate with and without RDFs as well as multivariate with and without RDFs – were generated. Twelve factors such as topographical, hydrological, geological,
land cover and soil plus three RDFs are considered. The weight of index for
landslide susceptibility is calculated by using the landslide failure map, and susceptibility regions are categorized into four classes as very low, low, moderate, and high susceptibility to landslides. With the integration of
RDFs, boundary detection between high- and very-low-susceptibility regions are
increased by 7 % and 4 % respectively.

/pdf/efficacy-of-using-radar-derived-factors-in-landslide-lp1rm2e83b.pdf

Efficacy of using radar-derived factors in landslide susceptibility analysis: case study of Koslanda, Sri Lanka

The differential GPS (DGPS) technique is one of the most popular and comparatively accurate techniques available to enhance the positioning accuracy by minimizing most of the common errors However, the ultimate accuracy of the user location depends on the remaining non-common errors (multipath, receiver clock, and noise), which occur at the points of observation and reference Out of these errors, multipath is the most dominant and challenging error to predict and minimize Single frequency C/A code based GPS receivers are popular due to their comparatively low cost compared to dual frequency (L1/L2) GPS receivers This paper focuses on evaluating the effect of multipath error on single frequency C/A code based GPS positioning For the analysis, 72,000 continuous GPS observations with one-second interval under four different multipath environments were conducted by utilizing three geodetic GPS units Accordingly, the observations with more than 5cm on the 2D positional error, created by the effected multipath, were always less than 25% Here, an average of 16% of observations exceeded 20cm in 2D positional error Further, it was noted that the presence of multipath introduces significantly higher and comparatively lower 3D positional errors on DGPS observations This could be due to the compensation of negative and positive effects caused by the multipath and other remaining non-common mode errors at the reference and user stations In addition, C/A code based single frequency GPS observations were significantly influenced by multipath, not only by the close-by reflectors but also by the ground surface The effect of multipath was about 50% of the total 3D positional error for the four tested multipath environments

/pdf/the-effect-of-multipath-on-single-frequency-c-a-code-based-32fjo56t2w.pdf

Thilantha Lakmal Dammalage

Papers

Land-Use Change and Its Impact on Urban Flooding: A Case Study on Colombo District Flood on May 2016

Ionospheric total electron content response to September-2017 geomagnetic storm and December-2019 annular solar eclipse over Sri Lankan region

Performance Analysis of GPS Aided Geo Augmented Navigation (GAGAN) Over Sri Lanka

Efficacy of using radar-derived factors in landslide susceptibility analysis: case study of Koslanda, Sri Lanka

The Effect of Multipath on Single Frequency C/A Code Based GPS Positioning