Midterm 1 Flashcards
What is Remote Sensing
Obtaining info about an object, area, or phenomenon through the analysis of data acquired by a device that is not in contact with it.
Electromagnetic Spectrum
Cosmic Rays Gamma Rays 10^-6 microns X-Rays 10^-4 microns Ultraviolet 0.1 microns Visible .4 to .7 microns Near-IR 1 micron Mid-IR Thermal IR 10 microns Microwave 10 cm TV and Radio 100 m
Frequency
Cycles per second
Stefan-Boltzmann Law
All matter above absolute zero continuously emits EM radiation and the amount of radiation is a function of the surface temperature of the object
Black body
Hypothetical ideal radiator that totally absorbs and reemits all energy incident upon it.
Wein’s Displacement Law
As the temperature increases, there is a shift toward shorter wavelengths. (Causes Red-Shift because as objects in the universe recede they cool)
Remote Sensing Steps
Energy source Radiation and the atmosphere Interaction with the target Recording of energy by the sensor Transmission, reception, processing Interpretation and analysis Application
Types of Atmospheric Effects
Scattering
Absorption
Atmospheric Scattering
Rayleigh EM > particle
Mie EM = particle
No selective EM < particle
Rayleigh Scatter
EM > particle
Shorter wavelengths more susceptible
Why the sky is blue: because blue light scatters more.
At sunset and sunrise light goes through more atmosphere so more colors are scattered.
Causes of atmospheric absorption
Water vapor
Carbon dioxide
Ozone
Atmospheric Windows
Wavelength ranges that are trans missive of EM spectrum
Energy interactions with surface features
Reflection
Absorption
Transmission
Spectral Reflectance
The percent of incident energy that is reflected from a surface.
What causes different types of Reflection?
Surface roughness.
Specular vs diffuse reflectors.
Roughness is relative to wavelength.
Radiance
Brightness on the image - the sum of light coming from the object and atmospheric scatter.
EM Detection Methods
Photographic
Electronic
Photograph vs Image
Analog vs anything
Ground Truthing Goals
Interpretation aid
Sensor calibration
Information verification
Advantages of aerial photography
Improved vantage point Snap shot in time Permanent records Broad spectral sensitivity Resolution and geometric fidelity
Image focus parameters
Focal length
Distance between lens and object
Distance between lens and image plane
Color Infrared
Blue: blocked (black)
Green: blue
Red: green
IR: Red
Digital Photography
Use of a complex array of photodiodes to image individual pixels
Laser scanner
Emits an EM pulse and then reflected pulse is analyzed
Photogrammetry
Handheld camera and range pole.
Two images, both with range pose images.
Resolution
Minimum separation distance for observer to distinguish 2 objects
Flight line issues
Tilt
Altitude change
Crab
Velocity changed
Aerial photo notations
Fiduciary mark
Principle point
Multispectral Imagery
Acquisition of imagery by simultaneous scanning through several spectral bands.
Across-track scanning (whisk room)
Oscillating mirror scans at right angles to flight path.
Long strips of successive scan lines
Instantaneous field of view
Multi-spectral
Instantaneous Field of View
The area the scanner sees at any instant in time.
Cone angle
Spatial resolution distance increases at the edges of the image (equal to pixel size)
Pixel
Records the average spectral Reflectance of an area.
Along-track scanning (pushbroom)
Uses a linear array of stationary CCD detectors to image a swath beneath the platform as it moves forward.
Each detector looks at a single spectrum.
Spectral Resolution
The number, wavelength, and width of spectral bands used by the sensor
Multi-spectral: wide bands
Hyper spectral: narrow bands
Radiometric Resolution
The number of brightness levels a sensor can record within a given wavelength.
Measured in bits
Resolution balancing act
Small IFOV increases spatial resolution
Small IFOV reduces Radiometric resolution
Increasing Radiometric resolution reduces spectral resolution
Temporal resolution
A function of how often a sensor flies over the object of concern and obtains imagery
Thermal Scanner
3-5 microns and/or 8-14 microns
Quantum or photon detectors (rapid response)
Uses mirror
Emissivity
How well the object radiates energy compared to the black body
Forward-Looking IR (FLIR)
Oblique angles of the ground
Finding targets
