UTILIZING DOT GRIDS TO MEASURE AREAL CHANGE: REMOTE SENSING OUTREACH

Dot grids are often used to measure the area of an object using images. A dot grid transparency may be placed over the image and the dots that touch the object in question may be counted. By using the RF scale of the photo, in correlation with the dots, an area can be determined. To help ensure consistency of measures, the dot grid should be dropped randomly on the map around the given area. This should be done at least twice so that an average area can be determined.

Such a system may be readily adapted to the classroom, from middle school through high school for modules emphasizing mapping and areal change. This work portrays a series of images (before and after) in which different “changes” have occurred (changes in vegetation, snow fields, ice floes, flooding). The students are provided the images, background data on each image, dot grid transparencies and the RF scales for the various images. The students are asked to measure/determine the area (km²) of change from one image date to another and are also asked a series of critical thinking questions concerning the assessment of change. As an aid to ensure the students are onboard with the requirements of the module, an example is worked for them prior to the initiation of their portion of the module.

This activity was successfully utilized at a Science Olympiad for high school students for a “Remote Sensing” event emphasizing the Earth’s hydrosphere and is readily adaptable to other areas of emphasis and grade levels.