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Summary of the articles of Remote Sensing (GEO4-4408)
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Summary of the articles that needed to be studied for the course Remote Sensing (GEO4-4408).
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A Lecture notes basics of remote sensingRemote sensing is a technique to observe the earth surface or the atmosphere from out of space
using satellites (space born) or from air using aircrafts (airborne). It registers reflected or emitted
radiation.
1. Source of electromagnetic energy (often the sun)
2. Atmospheric interaction (distortion, absorption, scattering)
3. Earth’s surface interaction
4. The sensor
A remote sensing system can either be passive or active. Passive systems observe the radiation
reflected by the object of interest (Landsat or SPOT). Active systems combine the energy source and
the sensor (it sends out the signal and returns it RADAR).
The amount of energy emitted is mainly a function of the temperature of the object and is described
by the Stefan-Boltzmann law. It is only valid for blackbodies, ideal material that absorbs all the energy
that strikes it. With increasing temperature the total amount of radiant energy increases and the
radiant peak (λ max) shifts to shorter wavelengths, also known as the Wien’s displacement law.
Atmospheric scattering results from the interaction between radiation and gases and particles in the
atmosphere. There is non-selective scattering (all wavelengths scatter equally and is caused by
particles) and selective scattering (shorter wavelengths are scattered more, caused by smoke or
fumes).
- Rayleigh scatter: short visiblle wavelengths, Results in haze. Caused by very small particles.
- Mie scattering: caused by partles in the atmosphere the same size as the wavelength
Soils can either be: transmission (passes through), absorption (used as heat), emitted, scattered or
reflected.
, Albedo is the ratio of the total amount of EM energy reflected by a surface to the amount of energy
incident upon it. Spectral reflection is the ratio of energy reflected by a surface to the energy incident
on it in a specific spectral interval.
Sensors are tools for indirect image registration in contrast to conventional cameras. A sensor or
detector is a device that receives EM, coverts it into a signal and it presents it.
Scanners are a detector with a narrow field of view which sweep across the terrain, the parallel lines
are combined together to produce an image. There are four common types of scanning: cross-track,
circular, along-track and side scanning.
Multi-spectral scanner (MSS): an airborne or space borne remote sensing system that simultaneously
acquires images of the same scene at different wavelengths. It has two main advantages: 1) objects at
the surface have varying reflection behaviour and can more easily be recognized using several bands,
and 2) many objects do not reflect radiation well inside the visible spectrum so outside of this
spectrum is better to identify these objects.
It works as follows: a telescope directs the radiation onto a rotating mirror, which reflects the
radiation into the optics. The optics focus the radiation into a narrow beam, which is split into its
reflected and emitted components (goes to the thermal infrared detectors). A prisms is placed in the
path to split the reflected radiation and then a detector is used. There is a linear array pushbroom
and a whiskbroom (which has a rotating mirror).
Meteorological satellites: NOAA-AVHRR, NIMBUS, Meteosat (geostationair).
Earth resources satellites:
- Landsat: NASA. 1-9.
- SPOT: first earth observation satellite launched by an European country. Pushbroom. 1-7.
- Copernicus: Sentinel. 1: radar for all-weather day and night, 2: MSI
- TERRA with ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) and
MODIS (Moderate Resolution Imaging Spectroradiometer, which can measure photosynthetic
activity)
- IKONOS: first commercial satellite by Space Imaging.
- ENVISAT: part of ESA (European space agency) very large.
- ESR = Europeanremote sensing satellite. SAR-imaging radar.
- SMOS = soil moisture and ocean salinity
- SMAP = soil moisture active passive
- HCMM = heat capacity mapping mission
Airborne sensors: CAESAR, Daedalus, GERIS and AVIRIS and unmanned (drones)
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