Midterm 1 Flashcards by Nicole Ridgwell

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.

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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

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Frequency

Cycles per second

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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

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Black body

Hypothetical ideal radiator that totally absorbs and reemits all energy incident upon it.

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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)

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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

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Types of Atmospheric Effects

Scattering

Absorption

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Atmospheric Scattering

Rayleigh EM > particle
Mie EM = particle
No selective EM < particle

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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.

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Causes of atmospheric absorption

Water vapor
Carbon dioxide
Ozone

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Atmospheric Windows

Wavelength ranges that are trans missive of EM spectrum

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Energy interactions with surface features

Reflection
Absorption
Transmission

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Spectral Reflectance

The percent of incident energy that is reflected from a surface.

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What causes different types of Reflection?

Surface roughness.
Specular vs diffuse reflectors.
Roughness is relative to wavelength.

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Radiance

Brightness on the image - the sum of light coming from the object and atmospheric scatter.

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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