IMAGE AND GRID DATA SETS

The grids and images occupy a significant part of the data sets within the GEOID environment. Several of these data sets were collected as images. Others were gridded for easier use. The cell size in each data set was determined by either data point density or final disk space usage. All the data sets in this category are projected. Projecting them on the fly would take too long. The projection used is Equirectangular, which is also the default projection in GEOID. The data sets can be accessed from the main menu by pressing the "Images/Grids" button. The projection is set to Equirectangular automatically; if it is set to some other projection a warning message is displayed. Figure 33 shows the Images/Grids menu.
 



Topography

On top of the list is the topography data which include submarine bathymetry as well. The cell size of this data set is 2 km. However, the original topography data had a resolution of 1 km. The bathymetry data came from two different data sets, one with about 3 km cell size beneath most of the oceans, and the other with 10 km cell size covering the polar regions. We merged all these data sets and generated a 2 km cell sized data set, hence subsampling the land areas and over sampling the bathymetry. Figure 34a shows of this data set. We also created a hill-shaded representation of the topography. This representation allows the relief to be highlighted, and it is convenient for display purposes. Figure 34b shows the shaded relief version of this data set.



Eurasia Basement Map

The Eurasia basement map covers, as its name implies, most of Eurasia. It is from the former Soviet Unionís IPE (Institute for the Physics of the Earth) maps. The data were gridded to a cell size of 10km. Figure 35 shows part of this data set in the Middle East and North Africa region.
 

 



Eurasia Moho Map

The Eurasia Moho map is similar to the Eurasia basement map in its source, spatial extent and cell size. Both the basement and Moho maps can be used for continental scale applications. Using them in regional and local studies may be misleading due to their nature. They are averaged and simplified and there is not an independent way of checking the quality of the reported values. Figure 36 shows the Moho values in the Middle East and North Africa region.
 



Cornell basement

This data set was developed entirely at Cornell for the Middle East region. Results from several published works as well as original work in Syria were used in generating this data set. The refraction and gravity profiles taken from the literature is shown in Figure 22a. Figure 37 shows the basement values and geographic extent of the data set.
 
 



Cornell Moho

The Cornell Moho data set is also entirely developed at Cornell using several data sets including the profiles shown in Figure 22a, gravity maps, surface wave tomography results, and receiver function studies. Figure 38 shows the Moho values and the geographic extent of the data set. This is the most reliable Moho map in this region. The values can be confirmed with published data sets and other studies.

 



University of Colorado Basement

This data set was obtained from surface wave tomography studies by the University of Colorado group. The data set covers much of Asia including parts of the Middle East. Figure 39 shows this data set and its geographic extent.

 
 



University of Colorado Moho

This is also a data set obtained from surface wave tomography by the University of Colorado group. The data set also covers an area in Asia with some Middle Eastern coverage. Figure 40 shows this data set.
 
 
 



Lg Coda Q values.

Lg coda Q values are obtained for Eurasia by the St. Louis University research group. The values were obtained after a tomographic inversion. Q values represent the efficiency of Lg wave propagation in the crust. Figure 41 shows the Lg coda Q values in the Middle East region.
 
 



 Pn velocity

Seismic Pn phase velocities were obtained from the New Mexico State University research group. The data set was obtained using a Pn tomography technique in the Middle East region. The values represent variations from a base velocity of 8.0 km/s. Figure 42 shows the data set and its geographic extent.
 
 
 



 Bouguer gravity data of the Middle East and North Africa

These Bouguer gravity data were obtained by gridding the point data provided to us by the Defense Mapping Agency. We are not at liberty to disclose the locations that were used in gridding. However, a secondary data set is provided under the Metadata section to represent the variance of the grid provided. Figure 43 shows the Bouguer gravity map.

 



Free air gravity data of the Middle East North Africa

These Bouguer gravity data were obtained by gridding the point data provided to us by the Defense Mapping Agency. We are not at liberty to disclose the locations that were used in gridding. However, a secondary data set is provided under the Metadata section to represent the variance of the grid provided. Figure 43b shows the Bouguer gravity map.
 
 
 


TM images

We currently hold a data set of about 100 TM scenes in the Middle East and North Africa region. A selection of these scenes is now available in GEOID. The Original TM scenes are about 30 m resolution. The data sets in GEOID are subsampled versions of these data sets. The new cell size is 285 m. The scenes were registered and a mosaic was formed. The scenes cover two regions: one in the Atlas mountains of North Africa, and the other in the Northern Arabian plate. Figure 44 shows the mosaic over the Middle East region. The other scenes are being processed and registered.
 


Add a color bar

Add color bar tool is used with the grid to add a color bar for the display images.  The user can choose the location where the color bar will be placed as well as the labeling parameters such as the increament size, label values, and label color.
Some of the images shown above used this tool to add a color bar.



The Profile Maker

The profile maker is a tool developed at Cornell to extract profiles or cross sections from the gridded data sets. The profile maker can be used to extract cell values along a transect, or it can be used to construct crustal scale cross section including topography, basement, and Moho values. Clicking on the "Profile Maker" button initiates a new sub menu and redraws the screen. The screen is divided into two sections: one to plot the map and the other to view the profile (or cross section) values. In the Profile Maker menu first the grids need to be selected from the "Select the grids" menu (Figure 45). Then two points locations representing the beginning and end points of the profile need to be entered. This can be done by either entering the values in the text entry locations or by selecting the "Select 2 points from the screen" button and marking two points on the screen. Following this, pressing on the "apply" button would extract the requested profile or cross section. Figure 46a shows a sample output of a cross section obtained using the topography data across south America. A great circle path approximation is applied between the points, so that the distance along the profile is the minimal distance. The extracted profile can be saved in an ascii file or plots of the map and the cross section can be made using the hardcopy button.   Another cross section involving topography, basement, and Moho is shown in Figure 46b. Another example of Lg coda Q values (crustal) from England to Iran is shown in Figure 46c.
 

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