Remote Sensing Unit 1

active remote sensing

an electromagnetic ray is emitted, then reflected back to a sensor and recorded

LiDAR

a form of active remote sensing; laser emitter and sensor units are attached to aircraft, which aims lasers at the ground and records the time it takes for the laser to bounce back to convert to point clouds

point cloud

a discrete set of data points in space which may represent a 3D shape or object

ground penetrating radar (GPR)

a form of active sensing; consists of a transmitter, a receiver, and antennae that are used to see below ground without excavating pits

passive remote sensing

sensing that uses the sun’s energy reflecting off the earth to a sensor

satellite digital imagery

a form of passive sensing; landsat and other satellites take images of the Earth’s surface using measurements of actual reflectance values, including both visible and non-visible bands of the EM spectrum

pixel

the smallest area that makes up a component of a digital image; larger pixels = less refined detail = larger area

resolution

the amount of information available in a satellite imagery; higher resolution = smaller pixel = finer detail

multispectral remote sensing

sensing based on the principal that energy from the sun is broken up into multiple components (ie colors/light spectrum)

wavelength

the distance between successive crests of the wave, typ. in m, cm, mm, etc

frequency

the number oc oscillations completed per second measured in hertz (Hz)

gamma rays

>ten-trillionths of a meter wavelength w/ extreme penetrating capabilities generated by radioactive atoms

x-ray

10-billionths of a meter to 10-trillionths of a meter wavelength w/ great penetrating power and extensive medical applications

ultraviolet rays

wvl of 400-billionth to 10-billions of a meter that can burn skin and are largely blocked by the ozone layer

visible rays

400-700 nm wavelength, best for identifying objects by visible colors

infrared rays

wavelengths extend from visible range to 1mm, including thermal radiation, with applications in locating thermal pollution and crop health

microwave radiation

range from 1mm to 30cm used for heating food and radar weather applications

radio waves

range from >1 cm to tens or hundreds of meters, used to transmit radio signals and create images through darkness or clouds

spectral irradiance

come back

spectral irradiance

come back

transmission

the movement of light through a material; length dependent

reflection

the process of radiation bouncing off an object; angle at which radiation hits and obect = radiation is reflected at the same angle

absorption

EM energy is absorbed and converted int another form of energy; tends to occur in absorption bands

scattering

the unpredictable reflection of radiation by atmospheric particles; largely occurs high in the atmosphere

refraction

the bending of light when it passes from one medium to another; dependent on angle with vertical, distance through mediums, and air density

diffuse reflection

combined diffuse and partial specular possible depending on the surface

apparent optical property (AOPs)

a property that can be explained as a function of two inherent optical property (e.g. reflectance (R = scattering/(absorption+scattering)))

inherent optical properties (IOPs)

cannot be explained as a function of other properties (e.g. absorption and scattering)