count dots inside lake and black dots on edge, measure grid cells with dots and convert and divide by 4. Total dots * grid per dot area = #m2 = # hectares.
[determining surface area of a feature]
equally spaced parallel lines that define narrow strips across the features. Construct perpendicular lines that define the edges of the feature with the strips. Measure the length of the strips and sum them. Multiply total strip length with strip width.
[determining surface area of a feature]
Tracing the edges with the lens and trading points. Tool.
Coordinate Methods using a coordinate system
Coordinate Methodsusing a coordinate system of (x1,y1). Area = (x1 +x2)*(y1+y2)....
give each column and row numbers. Then with in the those rows and columns count how many cells are being used of that area, and sum. Then multiply cells by that row or column number and sum, this is the product. Take the sum of product/by the sum of cells, this gives your x and y coordinates.
[volume of a feature]
given elevation, randomly place points within that contour lines.
Give the elevations of those points estimate the average and then subtract from base elevation to obtain average height.
Slab Summation Method
dissecting the elevations a slab at a time. Take the middle measure frothe base then multiply be the difference of the top slab by the bottom. The top slab is in a shape of a cone with a volume of 1/3π*R2h.
H = cone height, πR2 = area of circular base.
[volume of a feature]
taking the shape and consturcting a circle with that shape using itscentroid. Shape = 1.0 [ overlap of circle and shape/ area of both]
Compactness: A x 4π / p2
compactness of shape often is desirable, because most efficiently serviced and defended.
Indexes are based on area and parameter.
Slope: vertical change in the land surface.
Rise/Run: y/x; elevation difference (rise) and ground distance (run), taking two points higher – lower/ ground distance.
Slope angle: degrees, tan-1(y/x)
Slope percentage: y/x * 100
maximum slope at a point on a surface.
Vectors: magnitude and directions.
gives differentcolors for different compass directions as well as degrees.
Finding constant slope paths
perpendicular to the contour lines, this is the steepest downhill route.
mapping out thecontour lines on a line graph
visibility may be showincorrectly when a vertically exaggerated profile is used in aprofile.
use frames. Cameras located in air planes. Before during the war pigeons, 1957 -U2 and now we have the SR-71 blackbird.
Black and white: panchromatic (all colors); shorter blue wavelengths scatter by atmosphere reduces clarity causing photo to look hazy. [forests, topographic, road building, recreation]
True-color: emulsion layers blue, green and red. [vegetation, soils, geologic mapping, surface water studies]
Color-Infrared: world war II, CIR film, sensitive to IR and visible light.healthy vegetation = higher the IR.
devices collect images of reflected or emitted energy from small portions of electromagnetic spectrum (spectrum bands). Short to long waves [visible light, near- infrared(IR), thermal-infrared (TIR), and microwave bands.]
Side looking airborne radar: (SLAR)
antenna to emit pulses of microwave energy (1-30 cm) and then measure the energy reflected back from landscape. Strength of returned signal converted to gray tones. Advantages: not dependent on external energy, all weather, day or night. Bright spot = specular reflector, smooth right angle.
most detailed, ground surface – 1,500 feet about ground. Small ground area at a large map scale.
less environmental detail, 1,500-10,000 feet.
10-20 miles,U2 & SR-71, larger ground area covered
record thermal-infraredenergy we sense as heat, no dependence on reflected visible light. Detect [ water pollution from power plants, industries using watercooling purposes, potential geothermal energy areas, edges of forestfires, boundaries of ocean currents, underground streams.] buildings giving off heat
point directly under the camera, near the ground surface
Conjugate Principal Points (CPP)
location of the principal point on the first photo located and plotted as a point on the second photo.
Digital Elevation Model
A sample of elevations or depths taken on a regular grid. Sometimes called digital terrain model (DTM)World
wide coverage - SRTM, ETOPO and GlobeUS
coverage - National Elevation Dataset
Shuttle Imaging Radar (SIR):
L bandside looking radar. Black and white to highlight terrain, faults,folds, drainage patterns.
Light Detection and Ranging (LIDAR)
Simply making lots of accurate distance measurements with a laser rangefinder.
Accurate laser rangefinders are commonly used as surveying instruments, measuring tapes, rifle scopes, even golf aids!
Distance is calculated by measuring the time that a laser pulse takes to travel to and from an object
Each laser pulse can produce multiple consecutive measurements from reflection off several surfaces in its path.
National Aerial Photography Program
Photo Id Number
Photo Acquisition Date
Determining Map Scale from Reference Material
((1/x)/(1/msd)) = pd/msd
x = msd *md/pd
Describe methods of calculating RF of an aerial photograph
method 1: 1/x =f/H > x = H/f ..H: flying height, f: focal point
Ex. x=H/f=(10,000 ft x 12in/ft)/6in = 20,000
method 2: x= (alt.-elev.)/f
Ex. x= ((10,000ft -2,000ft)x12in/ft)/6 in=16,000
method 3: 1/x = measured length or width/ standard length or width
method 4: x=msdxmd/pdex: same 2 road .3 in on photo & .6 in on 1:24,000 scalex = 24,000 x .6 in/.3 in = 48,000
Radial Displacement Method
height of object (ho) = Hd/r
d= length of displaced object
r=radial distance from principal point
H=aircraft flying height
Shadow Method of Height Determination
ho/So = hx/Sx
hx = unknown feature height
Sx = shadow length of unknown feature
ho = known feature height
So = shadow length of known feature
h=Hdp / (P +dp)
Define: apparent displacement of objects when viewed from the perspective of different vantage points
= b1+b2 or (P1 +P2)
b1:the base of object to the principal point
b2: the base of object to the principal point
P1: principal point to the other principal point
P2: principal point to the other principal point
= (T1 -b1) + (T2-b2)
T1: top far corner of object to principal point
T2: top far corner of object to principal point
b1: the base of object to the principal point
b2 :the base of object to the principal point
Feature Identification elements:
shape, tone, color, size, height, shadow, pattern, texture, and site/situation.
most fundamental identification clue.
Decide if a shape is likely of natural or human origin.
Natural : irregular shapes
Human: simple geometric forms (straight sides, sharp angles, smooth curves)
object's lightness or darkness on the image.
tonal differences create contrasts which are fundamental to feature detection and identification.
Thermal: amount of radiant thermal energy detected by sensor [thermal capacity (amount of energy it can store), conductivity (resistance to heating or cooling), inertia (rate at which it gains or loses heat)]
On side-looking RADAR images: amount of backscatter to antenna
dominant wavelengths of visible spectral energy received by our eye.
hue: spectral aspect of the phenomenon
saturation: brightness or intensity
potential problem images are available at a variety of scales.
Object size estimation.
relative heights of features may be crucial to your identification of their function and their setting.
relative position: object located on the side of a tall feature. (feature identification)
cast by environmental features are important image interpretation cues.
conifers: cone shape
Deciduous: oval shape
Repetition of certain spatial forms or relationships is characteristic of many environmental features.
Signal underlying process.
Represents order which has a cause.
individuals together have a shape, size, arrangement, shadow, and tone to create a pattern of tonal variation.
Range from coarse to fine.
Smaller and smaller = finer = disappear.
Site and Situation
Relation of an object to surrounding features can provide useful hints to its identity, and may be only way to recognize some objects.
Situation: means of anticipating what to look for on a image.
Gentle slope, spaced out evenly
Steep, close together, rapid
Concave,closely spaced at the top of the hill, with progressive widening, U shaped
Conves, widely spaced at the top and closely spaced down the hill
vertical, overlay, ticks point towards the bottom
a: valley; long and narrow area with a v-shaped
b: ravine; deep narrow steep sided valley formed by water erosion
two higher elevation hills between is a dip
Major Landforms Types
Uniformly sloping plain
Ridge and valley topography
Braided River channel
pattern of ever smaller, roughly circular, concentric contours that end at the summit.
Slopes: uniformly steep from summit to lower elevations
Snowfields near the summit are visible
Radial pattern of roughly straight ski runs as cuts through the forests
straight streams that radiate outward from the summit
consistent with volcanoes
Drift less area subject to continental glaciation, remnant of dissected plateau