Mohammad Hossein Ramesht; Leila Gorjii; Mojgan Entezari
Volume 18, Issue 70 , August 2009, , Pages 16-19
Abstract
For more than half a century, soil erosion prediction and modeling technology has been used as a valuable tool in protective design, engineering plans and research development. This technology includes mathematical equations that calculate estimates of the dependent variables of erosion (soil losses, ...
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For more than half a century, soil erosion prediction and modeling technology has been used as a valuable tool in protective design, engineering plans and research development. This technology includes mathematical equations that calculate estimates of the dependent variables of erosion (soil losses, production and sediment) as a function of independent variables (four main factors: climate, soil, topography, and type of use). The parameters in these equations include exponential powers and coefficients that determine or modify the values of the independent variables as part of mathematical calculations, some of which are empirical values prepared according to basic data, while others have physical definitions associated with erosion processes. Mathematical symbols and logical sequence are among other features of mathematical models. In general, erosion mathematical models include regression-derived models, characteristic models, and process models. In addition to empirical methods, several mathematical models are presented concerning erosion, in all of which mass conservation law or the continuity equation are used as the controlling equation. These models include the dynamic and static models, the weep model, GULTEM and EGEM model, each of which is related to a particular type of gully and is applicable in certain conditions. Undoubtedly, the models introduced in this paper can not be considered as comprehensive models without any probable defects. Therefore, it is suggested that according to the climatic, geological, geomorphological, and ... characteristics, a suitable model be determined for assessing the rate of gully erosion in each region.
Abdollah Seif; Mojgan Entezari
Volume 17, Issue 66 , August 2008, , Pages 35-42
Abstract
There have been many ways of collecting data from a long time ago. Astronomical observation of land surveying, hydrography, photogrammetry and remote sensing are the main methods of location-based collection of information. Radar remote sensing is an interesting and special issue that reveals different ...
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There have been many ways of collecting data from a long time ago. Astronomical observation of land surveying, hydrography, photogrammetry and remote sensing are the main methods of location-based collection of information. Radar remote sensing is an interesting and special issue that reveals different aspects of remote sensing. Radar sensors called active sensors can capture images in almost all conditions, and obstacles like rainfall, cloud and night can not cause them any trouble. The term radar, which is used today throughout the world, has become an international term like radio and television. In fact, radar invention has been taken from a very natural physical phenomenon called reflection. Radio and electromagnetic waves are also capable of reflection, and the radar is based on this simple property. The simplest radars were actually formed by a transmitter and a radio receiver. Radar is an electromagnetic system that is used to detect and determine the target’s position. With the help of the radar the inside parts of environments like darkness, rain, snow mist, dust, and … that are impenetrable to the eye become visible. However, the most important advantage of the radar is its ability to determine the distance from the target’s range. The application of radars is for ground, air, marine, spatial and meteorological targets. Fabricating a high-capacity system for tracing phenomena and creating high-quality images of them is the main goal of the construction of imaging radar. In this article, we have tried to introduce active sensors in general to emphasize on radar systems and the mechanism of their operation, and to introduce the features of these images and provide a ground for more applied research in the future.