Remote Sensing and Digital Image Processing

Comprehensive vocabulary flashcards covering sensor and platform characteristics, digital image processing fundamentals, geometric corrections, radiometric calibration, and image enhancement techniques.

Sensor

The instrument or device that makes remote sensing measurements, such as a radiometer, spectrometer, LiDAR, or Synthetic Aperture Radar.

Platform

The type of vehicle that supports or carries a remote sensing sensor, such as a satellite, space shuttle, airplane, helicopter, balloon, or ship.

Geostationary Orbit

An orbital pattern where a satellite lies on the plane of the Earth's equator and travels at the same angular velocity as the rotation of the Earth, appearing stationary relative to the surface and maintaining a constant view of a specific area.

Polar Orbit (Sun-Synchronous)

An orbital pattern where a satellite moves around the Earth's poles from north to south, typically inclined from $8^\text{o}$ to $10^\text{o}$, passing over the same point on Earth only after several days under constant illumination conditions.

Framing System

A remote sensing system category that instantaneously acquires an image of an entire area or frame on the terrain, such as conventional cameras or Vidicon television cameras.

Scanning System

A remote sensing system category that employs a sensor with a narrow Instantaneous Field of View (IFOV) sweeping over the terrain to optically scan and electronically record reflected radiance line by line.

Across-Track Scanning (Whiskbroom)

A scanning mode that scans the Earth in a series of lines perpendicular to the flight path using a rotating mirror to sweep across the swath from one side to the other.

Along-Track Scanning (Pushbroom)

A scanning mode that uses a linear array of detectors at the focal plane pushed forward by the platform's motion to record successive scan lines, eliminating moving mirrors and increasing sensor lifespan.

Spatial Resolution

The fineness of spatial detail visible in an image, representing the size of the smallest object that can be resolved on the ground, bounded by pixel size.

Spectral Resolution

The ability of a sensor to define fine wavelength intervals within the electromagnetic spectrum that it can detect and record.

Radiometric Resolution

The sensitivity of a sensor to detect and record fine changes in electromagnetic radiation intensity or brightness levels, determined by bit quantization (e.g., $12\text{-bit}$ quantization yields $4096$ brightness levels).

Temporal Resolution

The revisiting frequency of a satellite sensor specifying how often it captures imagery for a specific geographic location.

Digital Image

A two-dimensional representation formed by a fixed array of rows and columns of picture elements (pixels), storing brightness values in numerical form.

Pixel

The smallest individual element in a digital image, holding quantized values (Digital Numbers / Brightness Values) representing brightness at a specific row and column address.

Instantaneous Field of View (IFOV)

The angular cone that defines the smallest area viewed by a sensor at a given instant, establishing the lower limit for spatial detail.

Dwell Time

The time interval allowed for a detector to focus on a ground area to accumulate enough photons to generate a strong electronic signal.

Band Interleaved by Pixel (BIP)

A digital image data storage format where spectral values for all bands are written sequentially for one pixel before moving to the next pixel.

Band Interleaved by Line (BIL)

A digital image data storage format where line values for all spectral bands are written sequentially before moving to the next scan line.

Band Sequential (BSQ)

A digital image data storage format where each spectral band is saved separately as an entire individual image file or channel.

Additive Color Model

A color visualization model based on combining red, green, and blue primary light sources (yielding white when combined at maximum intensity) used in computer displays and photography.

Subtractive Color Model

A color visualization model using cyan, magenta, and yellow primary pigments to subtract light wavelengths, primarily used in printing and painting.

Pre-processing

The initial digital image processing phase required prior to main data analysis, focusing on removing systematic errors, geometric distortions, and radiometric flaws.

Geometric Correction

Pre-processing operations that correct spatial distortions caused by Earth rotation, platform instability, oblique viewing, and terrain relief, transforming images into real-world geographic coordinates.

Cross-Track Scan Error

A tangential geometric distortion inherent to whiskbroom scanners where pixel ground size increases with the scan angle off nadir, stretching features toward swath edges.

Panoramic Distortion

A geometric distortion caused by regular sampling across a curved scan arc, making ground coverage proportional to the tangent of the scan angle and producing curved swath edges.

Scan Skew

A cross-scan geometric distortion caused by the forward movement of the satellite platform during the time taken by a scanning mirror to complete one sweep.

Ground Control Point (GCP)

A specific pixel location on an image whose corresponding ground coordinates (e.g., latitude/longitude or map coordinates) are precisely known.

Orthorectification

A form of geometric rectification that utilizes a Digital Elevation Model (DEM) to remove terrain and relief displacement errors from imagery.

Georeferencing

The process of assigning real-world map coordinates to digital image data.

Rotation, Scaling, Translation (RST) Transformation

A simple linear affine transformation algorithm using 3 or more GCPs to correct image position, scale, and orientation without accounting for internal skew or shear.

Polynomial Transformation

A geometric warping approach using regression equations of various degrees to map image coordinates to ground coordinates, correcting complex non-linear distortions.

Rubber-Sheeting

A non-linear, triangle-based geometric transformation method that stretches localized regions of an image to fit GCP coordinates across complex distorted scenes.

Root Mean Square Error (RMSE)

A statistical metric quantifying geometric rectification accuracy by calculating the distance difference between a GCP's predicted location and its actual reference coordinate.

Nearest Neighbor Resampling

A spatial resampling method that assigns an output pixel the Digital Number of the closest input pixel, preserving original radiometric values but producing a stair-stepped visual appearance.

Bilinear Interpolation Resampling

A spatial resampling method that calculates output pixel values using a distance-weighted average of the $4$ surrounding input pixels, generating a smoother image while altering original DNs.

Cubic Convolution Resampling

An advanced spatial resampling method evaluating a weighted average of the $16$ surrounding input pixels to calculate output values, delivering sharp yet smooth visual results at high computational cost.

Radiometric Correction

Corrections applied to raw Digital Numbers to eliminate or diminish unwanted variations in scene radiance caused by atmospheric conditions, solar illumination angles, and detector noise.

Line Striping (Banding)

A systematic radiometric artifact caused by drift or response variations among individual detectors in a multi-detector array, corrected using per-detector histogram matching.

Line Drop

A radiometric defect resulting from a completely dead or malfunctioning detector outputting zero values across a scan line, restored by interpolating values from adjacent lines.

Rayleigh Scattering

Atmospheric scattering occurring when atmospheric gas particles are much smaller than the wavelength of incoming solar radiation, predominantly scattering shorter blue wavelengths.

Absolute Radiometric Correction

An analytical calibration process converting raw Digital Numbers ($\text{DN}$) into true ground surface reflectance ($\rho_s$) by accounting for atmospheric optical depth and sensor calibration constants.

Empirical Line Method

An absolute radiometric correction method that correlates recorded sensor radiance against ground-measured surface reflectance over spectrally stable, dark and bright invariant field targets.

Haze Reduction (Contrast Reduction Method)

An atmospheric correction technique that identifies path radiance ($L_P$) over zero-reflectance targets (such as clear deep water in NIR) and subtracts that constant offset from all pixels in the band.

Sun Angle Correction

A radiometric calibration technique normalizing seasonal solar illumination differences across multi-date imagery by dividing Digital Numbers by the sine of the solar elevation angle ($\text{DN}_{\text{corr}} = \frac{\text{DN}}{\frac{1}{\text{csc}(\text{solar elevation})}}$).

Relative Radiometric Normalization

A calibration technique that adjusts the radiometric properties of a subject image to match a chosen reference image based on linear regression of invariant scene targets.

Cosine Correction

A statistical-empirical topographic normalization equation ($L_H = L_T \times \frac{\text{cos}(sz)}{\text{cos}(i)}$) that models direct solar irradiance over sloped terrain under the assumption of a Lambertian surface.

Image Enhancement

Digital operations performed to increase apparent contrast and intelligibility of image features for visual manual interpretation, without aiming for strict numeric analysis.

Spatial Domain

An image processing environment where enhancement operations directly manipulate pixel Brightness Values, either individually (point operations) or within local pixel neighborhoods.

Convolution Filter

A spatial filter where the output Brightness Value of a pixel is computed as a weighted average of surrounding pixels defined by a moving kernel matrix.

Spatial Frequency

The rate of change in Brightness Values per unit distance across an image, where smooth regions represent low frequency and sharp edges represent high frequency.

High-Pass Filter

A spatial filter that accentuates high spatial frequency components while removing low frequencies using a kernel with a high positive center surrounded by negative weights, sharpening edges and fine details.

Low-Pass Filter

A spatial filter that preserves low spatial frequencies while suppressing high-frequency noise by replacing center pixel values with the kernel average, producing a smoothed image.

Median Filter

A non-linear order statistics filter that ranks pixel values inside a window and replaces the center pixel with the median value, effectively removing impulse noise while preserving sharp edges.

Image Histogram

A graphical bar plot displaying pixel Brightness Values on the horizontal axis against the number of pixels containing those values on the vertical axis.

Linear Contrast Stretch

A contrast enhancement method that expands narrow raw Digital Numbers linearly across the entire $0\text{--}255$ display scale, mapping minimum input BV to $0$ and maximum input BV to $255$.

Histogram Equalization

A non-linear contrast stretch technique that redistributes pixel values so that densely populated histogram peaks are expanded, allocating roughly equal numbers of pixels to each output gray level.

Band Ratioing

A spectral enhancement technique created by dividing Digital Numbers of one spectral band by another ($\text{DN}_{\text{ratio}} = \frac{\text{DN}_{\text{Band A}}}{\text{DN}_{\text{Band B}}}$), effectively suppressing atmospheric, illumination, and shadow variations.

Normalized Difference Vegetation Index (NDVI)

A standardized vegetation index computed as $\text{NDVI} = \frac{\text{NIR} - \text{R}}{\text{NIR} + \text{R}}$, widely used to quantify green vegetative canopy vigor and biomass.

Enhanced Vegetation Index (EVI)

A vegetation index developed for MODIS that incorporates blue band reflectance to correct for atmospheric resistance and soil background reflectance in dense canopy conditions.

Soil-Adjusted Vegetation Index (SAVI)

A vegetation index incorporating a soil brightness correction factor $L$ (typically $L = 0.5$) to minimize soil background spectral interference in areas with low vegetative cover.

Principal Components Analysis (PCA)

An orthogonal linear transformation that rotates correlated multiband spectral axes into uncorrelated component axes, concentrating maximum data variance into the first principal component.

Pan-Sharpening

A data fusion procedure combining high-spatial resolution panchromatic image data with lower-spatial resolution multispectral data to generate a high-resolution color composite image.