GLG 362/598 Geomorphology

# Aerial Photography and Topographic Map interpretation and Geomorphic Mapping

## Introduction

The main parts of this lab come from Exercises in Active Tectonics:  An introduction to Earthquakes and Tectonic Geomorphology, by Nicholas Pinter, Exercise 3.

## Why?

These are essential tools.  You probably already know these things, but this is a good review.
Mapping makes you notice what is there.

## Scale

If  your pencil tip is 0.5 mm in diameter, how big on the ground is it if you are mapping on a 1:24,000 scale map?  How about a 1:500,000 map?

## Topographic maps

Show distribution of elevation in a region via contours (lines of equal elevation)
1:24,000 scale is typical for many places, but sometimes 1:200,000 or smaller is all that is possible.

## Aerial Photography

Form of remote sensing and powerful tool for many geomorphic investigations

## Mapping and image interpretation

### Basic Elements of Air Photo Interpretation--From U. Texas link above.

"Novice photo interpreters often encounter difficulties when presented with their first aerial photograph. Aerial photographs are different from "regular" photos in at least three important ways:
1) objects are portrayed from an overhead (and unfamiliar) position.
2) very often, infrared wavelengths are recorded, and
3)  photos are taken at scales most people are unaccustomed to seeing

These "basic elements" can aid in identifying objects on aerial photographs.

Tone (also called Hue or Color) -- Tone refers to the relative brightness or color of elements on a photograph. It is, perhaps, the most basic of the interpretive elements because without tonal differences none of the other elements could be discerned.
Size -- The size of objects must be considered in the context of the scale of a photograph. The scale will help you determine if an object is a stock pond or Lake Minnetonka.
Shape -- refers to the general outline of objects. Regular geometric shapes are usually indicators of human presence and use. Some objects can be identified almost solely on the basis of their shapes.
-the Pentagon Building
-(American) football fields
-cloverleaf highway interchanges
Texture -- The impression of "smoothness" or "roughness" of image features is caused by the frequency of change of tone in photographs. It is produced by a set of features too small to identify individually. Grass, cement, and water generally appear "smooth", while a forest canopy may appear "rough".
Pattern (spatial arrangement) -- The patterns formed by objects in a photo can be diagnostic. Consider the difference between (1) the random pattern formed by an unmanaged area of trees and (2) the evenly spaced rows formed by an orchard.
Shadow -- Shadows aid interpreters in determining the height of objects in aerial photographs. However, they also obscure objects lying within them.
Site -- refers to topographic or geographic location. This characteristic of photographs is especially important in identifying vegetation types and landforms. For example, large circular depressions in the ground are readily identified as sinkholes in central Florida, where the bedrock consists of limestone. This identification would make little sense, however, if the site were underlain by granite.
Association -- Some objects are always found in association with other objects. The context of an object can provide insight into what it is. For instance, a nuclear power plant is not (generally) going to be found in the midst of single-family housing. "

### Stereoscopic viewing

IC Power controls 3D aerial photography (nice demo of stereo viewing)

## Geomorphic mapping

Very important means of establishing landforms, their distributions and relations to eachother, process distribution, and history.
I can't work on anything unless i map it first!

### Mapping Mantras

1)  Even coverage:  if there is a blank space, you did not look there.
2)  Strive to provide detail.  Do not generalize.
3)  All lines mean something.
4)  Consistent notation and symbology.
5)  Quality control.  Dashing, line wts, queries.  Don't be wishy washy, but if something is uncertain or approximate, indicate so.
6)  Data/Ink ratio -> 1.  Put ephasis on important things (data) by putting relatively more ink in them--higher line weights, larger text, etc.)
7) Neatness counts.  Get some nice tools.

### Edward R. Tufte and visualizing information

Check out this link from my computers in geology class (http://geology.asu.edu/~glg410/Lectures/GLG410-charting.html)

## Photogrammetry and digital imagery

This is the direction things are going.  Points made above apply.
Look at this link for some advanced stereographic analysis by one of the students in my research group:
http://activetectonics.la.asu.edu/carrizo/DBmovies.html

Nice pages from the University of Wisconsin with the basics of aerial photography

## Lab assignment (due at the beginning of Lab, September 7)

2) Do lab
3) Do supplemental exercise (extra handout)

GLG 362/598 Geomorphology

Page maintained by
Ramon Arrowsmith

Last update August 30, 2000