Remote Sensing Image Scale Tutorial Is one image scale larger or smaller than another?

1. DIVISION C NC Science Olympiad 2008 Coaches Institute Remote Sensing • Remote Sensing Image Scale Tutorial • Is one image scale larger or smaller than another? • Scale is a measure of how large a real world object is represented in the image, or map. • If a specific lake appears bigger in the original image than in another, then the original image has the larger scale. • Is the scale 1 : 3,000 larger or smaller than the scale 1 : 2,000 ??? • The scale 1 : 3,000 means 1 unit in the image equals 3,000 units in the real world. • Represent the scale as a fraction ... Convert 1 : 3,000 to 1 / 3,000 and 1 : 2,000 as 1 / 2,000. • Which fraction is larger ??? 1 / 3,000 or 1 / 2,000 ??? • The larger fraction ( 1 / 2,000 ) is the larger scale. • In the larger scale image, the target object is larger ( the measurement with your ruler is greater) than in the smaller scale image. October 24 – 25, 2008 rshighberg@bellsouth.net Slide 1

2. DIVISION C NC Science Olympiad 2008 Coaches Institute Remote Sensing • Remote Sensing Image Scale Tutorial • Determining the scale of an image. • Identify the real world distance between two points on the image, or the coverage of the image. • The coverage of many of the ASTER images is given in their descriptions ... As in “Image covers 24 KM by 36 KM”. • Metric measurements are automatically decimal, and are more straightforward to use in calculations. • If you will measure in metric units, converting the real world distance into metric units makes things much easier. • Identify the known REAL WORLD Distance. • Measure the length of the known feature in the image with a ruler. • Convert each distance into the same units. • If the real world distance was in Kilometers, convert that distance into the units used in your measurement (for instance centimeters) • (4) Divide the real world distance by your measurement. The answer provides you with the real world distance for your unit of measurement. If your units were identical, (say centimeters real world and centimeters in the image), the result will be the denominator of the scale proportion, as in 1 / (answer) or 1 : (answer). October 24 – 25, 2008 rshighberg@bellsouth.net Slide 1

3. DIVISION C NC Science Olympiad 2008 Coaches Institute Remote Sensing Remote Sensing Image Scale Tutorial Determining the scale of an image. Mt. St. Helens This ASTER image of Mt. St. Helens volcano in Washington was acquired on August 8, 2000 and covers an area of 37 by 51 km. The image is centered at 46.2 degrees north latitude, 122.2 degrees west longitude. Step (1) Convert the real world distance into centimeters ... (37 km) X (1,000 m/km) X (100 cm/m) = 3,700,000 cm Step (2) Divide the real world distance (3,700,000 cm) by the measured length from the image (12.5 cm) ... 3,700,000 / 12.5 = 296,000. 12.5 cm in image 37 KM Real World Step (3) The non-dimensional scale is ... 1 unit in the image equals 296,000 units in the real world, the non-dimensional image scale is 1 : 296,000. 51 KM Real World Step (4) To express the scale as cm in the image per km in the real world ... divide 296,000 by 100 cm/m and then by 1,000 m/km. (296,000cm) / (100 cm/m) / 1,000 m/km) = 2.96 km. The image scale is 1 cm = 2.96 km NOTE: measurements in this sample calculation may not match those from your printout due the size of paper you’ve printed, or automatic shrinking/stretching accomplished by your software and/or printer. October 24 – 25, 2008 rshighberg@bellsouth.net Slide 1

4. DIVISION C NC Science Olympiad 2008 Coaches Institute Remote Sensing • Remote Sensing Image Scale Tutorial • Using PROPORTIONS to determine the unknown scale of an enlarged or reduced image from an original image with a known scale • The REAL WORLD distance between two common points (or edges of image) is the constant between the two images. • If you take measurements on the image using metric units, your calculations will already be decimal values. • 4.13 cm is easier to use in calculations than 1-5/8 inches • Convert the original scale to a non-dimensional relationship. • 1-inch equals 250 feet becomes ... 1-inch equals 250 feet times 12 inches per foot ... 1-inch measured equals 3,000 inches in the real world • the non-dimensional scale is then ... 1 : 3,000 or 1/3,000 • (2) Set up an equivalence between the ground distance calculations • The measurement from the original image times the non-dimensional scale of the original image is equal to the measurement times the unknown scale of the enlarged/reduced image. • (3) Solve for the unknown scale • (4) Immediately do a logic test on the answer ... Is the answer larger/smaller than the original ... SHOULD IT BE? • If your answer is out of whack, the proportion was set up incorrectly. Inspect it and do it again. October 24 – 25, 2008 rshighberg@bellsouth.net Slide 1

5. DIVISION C NC Science Olympiad 2008 Coaches Institute Remote Sensing Remote Sensing Image Scale Tutorial Using PROPORTIONS to determine the unknown scale of an enlarged or reduced image from an original image with a known scale (Step 1) Set up equivalence between original and reduced images (12.5 cm) x (296,000) = (7 cm) X (unknown scale) (Step 2) Solve for the unknown scale (unknown scale = (12.5 cm X 296,000) / (7 cm) (Step 3) Solve for the unknown scale unknown scale = 528,571 ORIGINAL IMAGE Scale 1 : 296,000 (Step 4) The non-dimensional scale of the reduced image is ... 1 : 528,571 (Step 5) Is the computed scale logical ??? YES 12.5 cm in image 37 KM Real World 7 cm in image 51 KM Real World REDUCED IMAGE NOTE: measurements in this sample calculation may not match those from your printout due the size of paper you’ve printed, or automatic shrinking/stretching accomplished by your software and/or printer. October 24 – 25, 2008 rshighberg@bellsouth.net Slide 1