Remote Sensing for Agriculture: Principles and Applications PDF

GIS and Remote Sensing for Agriculture L5: Basic principles of remote sensing Prasadi Senadeera [email protected] GNR/FB11 1 Content 1. What is Remote Sensing...

GIS and Remote Sensing for Agriculture L5: Basic principles of remote sensing Prasadi Senadeera [email protected] GNR/FB11 1 Content 1. What is Remote Sensing? 2. Components of a remote sensing system 3. Remote sensing platforms 4. Principles of Remote sensing 5. Vision – Light - Electro magnetic waves 6. EM spectrum 7. EM energy interaction with matter 8. Measuring reflected EM energy 9. Spectral properties 10. Radiation interaction with atmosphere 11. Atmospheric windows 12. Atmospheric scattering 13. Active and passive remote sensing 2 What is Remote Sensing Remote : Not making physical contact but observing from a distance. Sensing : Obtaining information Remote sensing is the art, science, and technology of observing an object, scene, or phenomenon by instrument based technique at a distance without physical contact (Tempfiet al., 2001 Principles of Remote Sensing) The term “Remote Sensing”, first used in 1950 in USA by Ms. Evelyn Pruitt of the U.S. Office of Naval Research 3  Components of a remote sensing system D G A A – Energy source of illumination B – Interaction with the atmosphere B B C – Interaction with the target F D – Recording of energy by the sensor C E E – Data retrieval, storage and Distribution F – Interpretation, correction and analysis G – Applications 4 Remote sensing platforms It can be defined as the carrier for remote sensing sensors. 1. Ground-level platforms – Like cranes and towers 2. Aerial platforms – Like helicopters, high altitude aircraft, and low altitude aircraft. 3. Spaceborne platforms – Like space shuttles, geostationary satellites, and polar-orbiting satellites. 5 Satellite image (Sentinel 2) UAV (Drone) Image Ground-level Image 6  Sputnik 1 -1957 Soviet Union Landast -1( 1972) -9(2021) -USA Sentinel -1 (2014) – 6 (2020) - European Space Agency (ESA) https://www.pixalytics.com/satellites-orbiting-earth-2019/ 7 Principles of Remote sensing Detection and measurement of the radiations of different wavelengths which are reflected or emitted from the surface of distant objects or materials, which helps in their identification and categorization. It has four basic components to measure, which include: 1. Energy source 2. Transmission path 3. Target 4. Satellite sensor 8 Vision How are things illuminated? How do we see object in our human eye? Can we see object in dark? How can dogs/cats see things in dark? How X-rays see things in our bodies? Source of illumination 9 Light Light Behaves as a particle (1704 by Isaac Newton) Travels as a wave (1803 by Thomas Young) Light has two oscillating components Electrical energy Magnetic energy Hence, light is called as electro- magnetic energy (EM energy) 10 EM waves Wavelength (λ)– the length of one cycle of oscillation and measured in distance measurement units (e.g., m, mm, nm, or µm) Period (t) – time takes to complete one cycle and measured in seconds (s) Frequency (f) - the number of waves passing a fixed point in a specified period of time (1/t) and measured in Hertz (Hz = s-1) http://eqseis.geosc.psu.edu/cammon/HTML/Classes/IntroQuakes/Notes/seismometers.html Amplitude (α) – the peak value of the wave. 11 Wavelength(𝝀) vs Frequency(𝒇) Wavelength and Frequency is inversely proportional 1 𝑓 ∝ → 𝑓𝜆 = 𝐶𝑜𝑛𝑠𝑡𝑎𝑛𝑡 𝜆 EM waves travelling in speed of light (c) 𝑐 =𝑓𝜆 𝑐 ≈3 ×108 𝑚𝑠−1 Tempfi et al., 2001 – Principles of Remote Sensing 12 Wavelength(𝜆) vs Energy (𝑄) Energy is inversely proportional to wavelength and proportional to frequency 1 𝑄∝ → 𝑄𝜆 = 𝐶𝑜𝑛𝑠𝑡𝑎𝑛𝑡 𝜆 𝑄 𝑄 ∝𝑓 → = 𝐶𝑜𝑛𝑠𝑡𝑎𝑛𝑡 𝑓 So, in other way, 𝑐 𝑄 =ℎ ×𝑓 →𝑄 =ℎ× 𝜆 ℎ: 𝑃𝑙𝑎𝑛𝑐𝑘′𝑠 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 = 6.6262 ×10−34 𝑐 ≈ 3 ∗ 108 𝑚𝑠 −1 13 EM spectrum https://www.miniphysics.com/electromagnetic-spectrum_25.html 14  EM spectrum wavelengths By Inductiveload, NASA - self-made, information by NASABased off of File:EM Spectrum3-new.jpg by NASAThe butterfly icon is from the P icon set, File:P biology.svgThe humans are from the Pioneer plaque, File:Human.svgThe buildings are thePetronas towers and the Empire State Buildings, both from File:Skyscrapercompare.svg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2974242 15 Sources of EM energy The Sun: Prime Source of EM Energy Earth itself is source of EM Energy RS sensors measure, Reflected Emitted EM energy 16  EM energy interaction with matter Incoming energy Emission (ε) Reflectance (ρ) Incoming Energy: Sunlight (visible light, near-infrared, and thermal infrared) Absorption: The leaf absorbs visible light Absorption (α) for photosynthesis and a portion thermal infrared energy, raising its temperature. Reflection: Gives the color, Chlorophyll Visible and near- absorbs most of the red and blue Thermal infrared wavelengths of light from sunlight but infrared radiation: radiation: reflects the green wavelengths. 𝜶+ 𝝉+ 𝝆=𝟏 𝜺+ 𝝉+ 𝝆=𝟏 Transmission: passes through the leaf helping photosynthesis Transmission (τ) Emission: The leaf emits thermal infrared radiation as it re-radiates the absorbed energy as heat. 17. Measuring reflected EM energy Spectral Radiance (Lλ(θ,ϕ)): Radiant energy emitted, reflected, or transmitted by a surface in a specific direction (θ, φ) per unit area, solid angle, wavelength, and time. Φλ(θ, φ): total power of radiation at a specific wavelength. Ω: Solid angle subtended by the source as viewed from the sensor. A: Projected area of the surface (area perpendicular to the direction of the incoming or outgoing radiation). cos(θ): Accounts for the angle of incidence or emission relative to the surface normal © Lars Eklundh, LU, Sweden 18 Terminology Radiance (L)– the amount of energy being emitted or reflected from particular area per unit solid angle and per unit time. Unit is Wm-2sr-1 Spectral radiance (Lλ) – radiance per unit wavelength (Wm-2sr- 1µm-1) Irradiance (I)– the amount of incident energy on a surface per unit area per unit time (Wm-2) 19 Spectral properties We need to know the actual spectral properties of the object and it is not depending on the incoming light This Photo under by Unknown Author is This Photo by Unknown Author is licensed licensed CC BY-ND under CC BY-ND 20 Reflectance Reflectance is the proportion of incident electromagnetic (EM) radiation that is reflected by a surface. Measure of how much light or radiation a surface reflects compared to how much it receives Reflectance is independent of the illumination Reflectance is unitless 𝑅𝑎𝑑𝑖𝑎𝑛𝑐𝑒 (𝐿) 𝑅𝑒𝑓𝑙𝑒𝑐𝑡𝑎𝑛𝑐𝑒(𝜌) = 𝐼𝑟𝑟𝑎𝑑𝑖𝑎𝑛𝑐𝑒 (𝐼) 21 Radiation interaction with atmosphere https://www.usna.edu/Users/oceano/pguth/md_help/remote_sensing_course/atmos_transmit.htm 22 Atmospheric Window The portion of the electromagnetic spectrum that can be transmitted through the atmosphere. https://gisgeography.com/atmospheric-window/ 23 Atmospheric scattering - I Atmospheric scattering is the process where particles and gases in the Earth's atmosphere deflect and disperse incoming sunlight in different directions. Rayleigh scattering Very small particle O2 and NO2 Size of the particle