RVRV ^{bringing geospatial data analysis down to Earth}

A new application for ER Mapper in the field

John Cady is a consulting geophysicist specializing in the field analysis of geospatial data for mineral and petroleum exploration. He designed and built the RVRV -- an integrated GIS and GPS system that takes geophysical and other geospatial data to the field for in situ analysis and interpretation.

Common data used in RVRV applications include digital topography, Landsat TM images, aerial photography, geophysical and geochemical data. The data are first analyzed and interpreted in the office, using ER Mapper to overlay, combine, and query data from multiple sources. Questions left unanswered in the office are taken to the field as testable hypotheses: data and interpretations displayed on the RVRV monitor are compared to the real world outside the van. The full power of ER Mapper is available in the field to process and analyze pertinent geospatial data.

At a field site the computer, a rugged laptop computer with attached GPS, is undocked from the vehicle and carried on foot. For example, a geologist walks a geologic contact or fault, laptop in hand, guiding his or her traverse using an image that combines multiple data sets. Meanwhile, the computer records and displays the contact or fault as a GPS track. The geologist draws contacts as vectors on the computer image, as geologists have always done using pencil and paper. Observations, for example measurements of magnetic susceptibility on the outcrop, are automatically recorded and geocoded with the GPS location. The RVRV can also be implemented in a helicopter, fixed-wing aircraft, or watercraft.

URBAN DEMOGRAPHICS: A powerful feature of ER Mapper is the ability to combine multiple data sets into a single data set of many layers, then query the cells in those layers using algebraic and Boolean functions. Cady took 1990 US Census Data of the Denver metropolitan area and converted them to logarithms in Excel so that they could be accurately expressed as 8-bit grayscale images in ArcView. These were exported to ER Mapper and georegistered. Cady studied a phenomenon that could be observed directly in the field -- the age, type, and distribution of residential housing.

Figure 1 shows the housing density of greater Denver in 1939 and 1990, in color, superimposed on topography (30 meter cell size) displayed in 3-D perspective. Topographic relief is greatly exaggerated. Orange lines are county boundaries. The spreading orange and yellow areas show the suburbs of Denver sprawling out into former farmlands, shown in blue. Suburban growth selectively moved onto the higher ground, mainly stream terraces, while industrial areas concentrated along the Platte River and Clear Creek.

Cady hypothesized that classic, individual architect-designed and owner-built homes were preferentially built on west-facing slopes of stream terraces having a view towards the Rocky mountains. He designed a process using ER Mapper and the RVRV that would enable him to "prospect" for these homes.

Figure 2 shows the change in housing density from 1939 to 1949 superimposed on shaded relief topography illuminated from the west. The colors show the increase in housing units per square kilometer from 1940 to 1949 on west facing slopes of more than two percent. Cady's working hypothesis was that fine homes would be concentrated in areas of moderate buildout, shown in blue and yellow, where individuals could buy choice lots in advance of mass development. In contrast, gray areas, either flat or east facing, should be dominated by mass-produced housing.

 The preceding story is from ER Mapper Magazine, Issue 1. My thanks to Helen Burdett, Editor of the Magazine, for permission to use the story on the GeoPeregrino website.

 RVRV is a trademark and service mark of John W. Cady dba GeoPeregrino.

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