CE 203 Midterm 1 (Spring) Terms

geomatics engineering

the science of the collection, analysis, and interpretation of data, especially sensor data, related to Earth’s surface

Remote

not in contact with, away from

sensing

the act of observation

Remote Sensing

a technology for sampling electromagnetic radiation to acquire and interpret non-immediate geospatial data from which to extract information about features, objects, and classes on Earth’s land surface, oceans, and atmosphere

black body

a perfect absorber and maximum emitter of radiation at a given temperature (ρ = τ = 0)

opaque object

τ = 0, ρ + α = 1

Green and NIR

Healthy vegetation REFLECTS what types of of the electromagnetic spectrum?

Red

Healthy vegetation ABSORBS what parts of the electromagnetic spectrum?

passive sensors

sensors that record the received signal from the surrounding environment (ex: RGB, multispectral, and thermal cameras)

active sensors

sensors that transmit signal and record the response from targets (ex: LIDAR, radar)

temporal resolution

the frequency of the return of the platform; determined by orbits and instrument characteristics

spatial resolution

spatial “area” represented by each data cell (displayed as a pixel); determined by the altitude of the platform and its sensor optics

dynamic range of the data

the number of bits used to represent the data (determines the amount of shades of gray in an image)

spectral resolution

“detail” by which spectrum is represented (the spectral range of each band); determined by the design of the sensor

planck’s law

the longer the wavelenght, the lower its energy content (the spatial resolution of sensors at a longer wavelengths is inherently lower)

spectral signature

reflectance and wavelength values that correspond to a specific kind of element (i.e. vegetation, water, etc)

band

range of wavelengths that a sensor absorbs

weather satellites

what satellites have high temporal resolution and coarse spatial resolution

geosynchronous orbit

a satellite orbit that synchronizes with the rotation of the Earth (always looks at the same thing)

geostationary orbit

geosynchronous orbit with an inclination of 0 (over the equator)

earth resource satellites

satellites that typically have medium spatial resolution and are near polar orbiting (ex: landsat)

high spatial resolution satellites

satellites used to gained specific data, often used for construction/site planning

map projections

a method to display Earth as a flat surface

mercator

a cylindrical mapping projection that is useful for mapping the equator (scale is only true at the Equator but increasing distorts as the map approaches the poles)

transverse mercator

a mercator mapping projection rotated 90 degrees (true at Greenwich meridian)

universal transverse mercator (UTM)

a mapping projection with longitudinal zones of 6 degrees each, with each zone having its own central meridian (minimizes distortion)

horizontal datum

a mathematical representation of Earth that is defined by the shape of a reference ellipsoid and location

vertical datum

an elevation reference defined from geoid models

geoid

the equi-potential surface that coincides with the Mean Sea Level (has irregular surface)

digital number (DN)

integer number related to intensity. Has no physical meaning & sensor calibration is required to convert to scientific units.

Radiance

Amount of radiation from a given area. DNs are transformed to this via sensor calibration

Reflectance

proportion of incoming radiation reflected from a surface as measured at the satellite; compensates for solar effects, still needs atmospheric correction (processed after radiance)

radiometric enhancement

techniques used to make an image more “interpretable” visually

thresholding stretch

a stretch where original values are thresholded over selected ranges and assigned to a small number of integer values

linear stretch

a stretch that converts original DNs to new values using a linear function; maintains the relative “position” of the data in the original histogram

histogram equalization stretch

a stretch that creates output histogram “equivalent” to uniform distribution (constant); can result in anomalies in the image

gaussian stretch

a stretch that maps the data into a gaussian such that the output has guassian (normal) distribution

min-max stretch

a stretch where the histogram is evenly stretched across the entire range

low pass filter

a filter than passes the low frequency information; emphasizes the large area changes in brightness; de-emphasizes local detail and smooths noise

high pass filter

a filter that de-emphasizes large area changes in brightness; emphasizes local detail

edge enhancement filter

a form of high pass filtering that specifically enhances edges

mean smoothing

a low pass filter that smooths noise, preserves local mean, but distorts the edges of the images

weighted smoothing

a low-pass filter where the greatest weight is on central pixel (e.g. Gaussian), preserves local mean, and de-emphasizes pixel values further from the center of the template

median smoothing

a low pass filter that preserves the local median, de-emphasizes anomalies, has less distortion around edges, and is good for impulse-like noise

gradient filter

a high pass filter that replaces the continuous derivative of brightness with differences (enhances edges in all directions)

unsupervised

a type of classification that does not require training data

supervised

a type of classification that requires training data

ISODATA

a unsupervised classification method where points are assigned to clusters based on which cluster’s mean point is closest to the point being classified

training data

data used for the classifier to estimate the characteristics of each class

test data

the data used to evaluate the accuracy of a supervised classifier

k-nearest neighbor

a method of supervised classification where the value of a pixel is assigned according to the majority label of the k nearest spectral neighbor training pixels

maximum likelihood

a supervised classification method that assigns pixels to classes based on the probability density plot of each class

decision boundary

the threshold between classes in maximum likelihood classification

producer’s accuracy

the accuracy of a class from the perspective of a map maker. Essentially, the number of correctly classified reference sites for a class / total number of reference sites for a class

overall accuracy

the percentage of all reference sites that were correctly classified

user’s accuracy

how often the class of the map will be present on the ground (reliability). Essentially, number of correctly classified sites / total number of classified sites

kappa statistic

a measure of agreement adjusted for chance agreement

scale of maps

distance on a map / distance on the ground

scale of a vertical photograph

distance on image plane / distance on the ground

nadir point

point on the ground directly below the camera

principal point

the center of the focal plane

flying height

distance above the ground

principal distance

focal length

orthophoto

image with no relief displacement

relief displacement

the lateral displacement (also called as shift) in the position of image on the photograph of a ground object; occurs in the radial direction from the nadir

imaging systems

systems that acquire data over 3D phenomena; resultant output is 2D

photogrammetry

a process that inverts the process of photograpy to extract 3D phenomena

parallax

displace of the apparent position of an object with a frame of reference due to the shift of observation

x-parallax

the parallax along the base connecting the two perspective centers; also the parallax responsible for depth perception

y-parallax

the parallax along the perpendicular direction

LIDAR

an active sensor that transmits light to a target and that light’s reflectance is recorded back by the sensor

Overlap

Common area between successive images along the same flightline

side lap (lateral overlap)

common area between images along neighboring flight lines

ground sampling distance (GSD)

Extent of covered area by a single pixel

vertical image

an image whose optical axis is aligned along the gravity direction (plumb line)

GNSS

international GPS system

IMU

inertial measurement unit; measures pitch, roll, and yaw of the LIDAR unit; helps correct point cloud distortions due to sensor movement

ground reference GPS Survey

a GPS survey that provides “ground truth” reference data; used to estimate biases in LIDAR data

point void

gaps or missing data in a LIDAR pointcloud where no returns were recorded (caused by shadows, e.g. the pulse being blocked by a building)

DEM

a 3D gridded raster data and representation of terrain, each cell contains an attribute (e.g. height)

bare earth DEM

a DEM that only contains the ground (often equated to digital terrain models, which focuses on topography)

DSM

a 3D surface model of the earth, including natural topography, artificial structures, and vegetation

DBM

a 3D model of only the buildings in the area

control segment

the segment of the GPS system that uploads data to the satellites

space segment

the segment of the GPS system that contains the satellites; broadcasts data to the user segment

Baseband signal

the original GPS data signal containing navigation information (e.g. satellite position, timing data, and correction factors); it is a low frequency signal that needs to be modulated for efficient transmission

carrier signal

a high frequency sinusoidal wave used to carry the baseband signal over long distances; allows for efficient transmission and reception of the GPS signal by reducing interference and enabling frequency multiplexing

modulation

a process where the baseband signal is combined with the carrier signal to prepare it for transmission

geocentric coordinate system

a three-dimensional cartesian cocrdinate system with its origin at Earth’s center of mass. X points towards the equator’s prime meridian, Y points 90° east of the X-axis at the equator, and Z points towards the north pole. Does not account for Earth’s shape variations

Geodetic coordinate system

a system that represents locations on Earth’s ellipsoidal surface using latitude, longitude, and ellipsoidal height. Accounts for earth’s shape variations

pseudo-range

the measured distance between a GPS satellite and a receiver, but it includes errors due to timing inaccuracies, atmospheric delays, and other noise sources.