SaLIS Vol. 63, No. 2

June 2004

 

Two-step Analysis of Nodal Point Stability in a Leveling Network in the Southwest of Israel

Gilad Even-Tzur

 

Repeated precise leveling surveys carried out during the past decade point to an instability of the nodal points in the leveling network in the southwest part of Israel. This situation prevents the adjustment of the leveling network to ensure correct heights for benchmarks. Modeling the regional and local vertical movements of points will enable adjustment of the leveling network, which contains lines that were measured in different times. Nine GPS campaigns were carried in the region over a period of one calendar year to monitor the stability of the network’s nodal points. The large number of monitoring sessions enabled the investigation of the fluctuations of the nodal points, based on physical processes such as the cyclic effects of swelling and shrinking of the ground.   The GPS measurements were analyzed by a two-step analysis. In the first step, geodetic measurements were processed sequentially without modeling variations in the height of the network’s points. In the second step, the variations in the network geometry were modeled by means of a physical model.

 

 

 

USDA/FSA Crop Compliance Monitoring GIS

Stacey D. Lyle, RPLS

 

Small-format digital aerial imagery is becoming an important source of data for crop compliance monitoring by the U.S. Department of Agriculture (USDA) Farm Service Agency (FSA). This paper describes the procedures required to establish a geographic information system (GIS) of common land units (CLUs) using small-format digital aerial images.

 

 

Mapping Groundwater Level and Depth in the Azraq Basin in Jordan Using GIS

Rida Ali Al-Adamat and Serwan M.J. Baban

 

Water resources can play a vital role in the economic development of a country. In Jordan, water resources are scarce and decreasing, and groundwater is considered the major water resource. The Azraq is one of the largest groundwater basins in Jordan, and it is currently facing an over-extraction problem. This study attempts to assess and map groundwater resources in the Azraq Basin using ARCVIEW GIS software. The relationship between land topography and depth-to-water surface was found to be statistically significant, while there was no significant association between land topography and groundwater level. Two essential thematic layers were created—depth to groundwater and groundwater level and the slope of groundwater level was mapped. The majority of the study area has a slope of less than four degrees with smaller scattered areas were the slope could rise up to 8.6 degrees. The results indicate that, due to the nature of the data involved and the analysis required, GIS could facilitate the necessary spatial digital analysis. Subsequently, its outcomes can be used for future groundwater planning and monitoring.

KEYWORDS: Groundwater, mapping, GIS, Jordan

 

 

 

Assessing Land Cover Changes in the Coastal Zone Using Aerial Photography

Raid Al-Tahir and Asim Ali

 

One important aspect in the management of the environment and its resources is establishing the spatial extent and the dynamics of changes in land cover and land use over time. This paper proposes a methodology for monitoring land cover change in coastal zones, specifically coastal mangrove wetlands. The approach was inspired by the availability of aerial photographs at several epochs and their high spatial resolution and geometric stability. The topographic features of coastal zones justify relaxing the rigorous and complicated procedure of photogrammetric orientation, while still achieving an adequate reliability and accuracy. The methodology developed in this paper is followed by a case study evaluating the validity and applicability of this technique in assessing changes in coastal mangrove forests.

 

 

Assessment of the Use of Remote Sensing Techniques for Locating and Mapping Ordinary High Water Lines for Lakes Kissimmee and Hatchineha in Florida

Scot Smith, Janet Nunley, Bon Dewitt, and  Levent Genc 

 

Determination of the ordinary high water line (OHWL) has been and continues to be an important issue for the State of Florida and elsewhere. The OHWL defines the separation of sovereignty lands of the State and private ownership on non-tidal water bodies. We used imagery from multiple sources to determine if: (1) the water’s edge can be detected around the lake margins and (2) vegetation community shifts can be reliably detected and correlated with OHWL. It was determined that in areas where water is known to be under vegetation canopy or in heavily vegetated marsh there were no distinct indicators of the OHWL on any of the remote sensing images used. This is because overhanging vegetation and emergent macrophytes both obscure the water’s edge. We also found that vegetation types varied widely and none appeared to be precise indicators of the OHWL   Most of the plant species in the vicinity of the known location of the OHWL were not classified in any one wetland designation and many were found both in wetland and upland areas and, therefore, provided no distinct characteristics that could be consistently identified or mapped in ArcView using remote sensing images.

 

 

The Astronomical Longitude of Paramaribo

Kenneth W. Blesch

 

In 1911, Van Stockum determined the astronomical longitude of Paramaribo from an absolute moon height in combination with star observations. This paper explores the notion and proves that the astronomical longitude of Paramaribo published by Roelofs in his book, Astronomy Applied to Land Surveying, is based on Van Stockum’s astronomical observations in 1911, corrected for precession and nutation.