1 Introduction Flashcards
What is Remote Sensing?
The science of obtaining information through the analysis of data acquired by a device without direct contact with the object.
History of RS
The history of remote sensing began with photography as cameras were the first sensors to be developed.
The remote sensing era began with aerial photography.
1972: Launch of Landsat 1, the first satellite dedicated to monitoring land and ocean resources.
Remote Sensing Applications
weather and climate
Urban RS (showing land surface temperature)
ship traffic management
Agriculture (different type s of agriculture)
Land cover mapping (different crop types)
Cryosphere (Digital Elevation Model)
Remote Sensing Sensors
Remote sensing uses the radiant energy that is reflected, emitted, or scattered from the Earth and its atmosphere from different parts of the electromagnetic (EM) spectrum
Sensors can be categorized as ACTIVE and PASSIVE based on their source of energy
Electromagnetic (EM) Spectrum
Our eyes are only sensitive to wavelength ~380 - 750 nm (visible light)
750nm red
380 nm purple
lamda = c/f where: lamda = wavelength f = frequency c= speed of light (3 x 10^8 m/s)
Sensors can measure different parts of EM (e.g. heat scanners measure infrared light emitted from the human body)
Spectral Signature
Variation of reflectance (or emittance) of a material as a function of wavelengths
Atmospheric Windows
- Only electromagnetic radiation in certain wavelength regions (atmospheric windows) can penetrate the atmosphere
- Other parts are absorbed or scattered by the atmosphere.
- Remote sensing sensors are designed to measure reflected or emitted light in atmospheric windows
How do digital images work?
# Digital image – is an image digitized into a sequence of numbers that the computer can understand – Each pixel has a column/row and 1 number (typically between 0 and 255) per channel. – High values bright, low values dark
# Additive RGB color model – Any color is created by mixing the three basic colors. – Color images have three channels: RGB = (Red, Green, Blue). – Remote sensing images can have one, several, or many channels.
Four types of Remote sensing image resolution
Temporal resolution (how often)
Spatial resolution (how small and detailed)
Spectral resolution (what colors or bands)
Radiometric resolution (color depth)
Four types of Remote sensing image resolution
- Temporal resolution
• The ability of the satellite to provide repeated images from the same area (revisit time).
• Sensors usually trade spatial resolution for temporal resolution.
–Landsat: 16 days temporal and 15 60 m spatial resolutions
–Modis: 1 day temporal and 250 1000 m spatial resolutions
Four types of Remote sensing image resolution
- Spatial resolution
# Size of the smallest feature that can be detected by a satellite sensor. – Defined by IFOV (Instantaneous field of view)
– IFOV is
• the angular field of view of the sensor
• independent of height
•a relative measure because it is an angle not length
– Ground projected instantaneous field of view (GIFOV) depends on satellite altitude (H)
– Usually expressed in meters
# Pixel size is defined by sampling distance – Resolution cannot be smaller than pixel size
Four types of Remote sensing image resolution
- Spectral resolution
Ability of the sensor to measure specific wavelengths of the electromagnetic spectrum (number of bands and their width).
–Panchromatic: one large portion of visible spectrum
–Multispectral: several small portions of spectrum
–Hyperspectral: many tiny portions of spectrum
–Higher spectral resolution allows better identification of certain land covers
Four types of Remote sensing image resolution
- Radiometric resolution
The ability of a sensor to discriminate slight changes in recorded energy.
– Computers store information as zero and one.
– Intensity of a pixel is digitized and stored as a finite digital number.
– Bit depth indicates the number of variations a pixel can store
