1. Basics of radiation physics for remote sensing of vegetation
UNIVERSIDADE DE SÃO PAULO
ESCOLA SUPERIOR DE AGRICULTURA
“LUIZ DE QUEIROZ”
DEPARTAMENTO DE GENÉTICA
LGN5831 Tópicos Especiais de Genética e Melhoramento
Basics of radiation physics for remote sensing of vegetation
Prof. Roberto Fritsche-Neto
Piracicaba, August 28, 2017

2. Absorption and reflectance

3. Remote sensing
Remote sensing is the collection of information (sensing) from an object or area from a distance (remote)
Source and detector are both remote

4. Types of remote sensing
a radar (or e.g., lidar) transmits and receives radio (or light) signals reflected back to itself
a microwave imager (or e.g., spectrometer) measures natural thermal radiation (or reflected sunlight)

5. Electromagnetic spectrum
The most useful in remote sensing of vegetation: Visible to SWIR
300 nm to 15 μm

6. Thermal remote sensing of the crop canopy
The Stefan-Boltzmann law states:
The emittance of radiation in the thermal infrared region of the electromagnetic spectrum by the crop canopy is proportional to its absolute surface temperature raised to the fourth power

7. Lambert’s Cosine Law - irradiance
The radiant flux received (irradiance) is related to:
The cosine of the angle z (θ = zenith angle) between the beam and a line normal to the surface

8. Incoming solar radiation
The illumination of a surface and radiation emitted from the surface may vary with time of day, season, wavelength, location, and atmospheric conditions

9. Incoming solar radiation

10. Radiation interacting with a material
Scattered radiation
need correction for this noise

11. Radiation is scattered by particles
scattering particle is
much smaller
same order as the wavelength
several times larger than the wavelength
Remote sensing of VIS/NIR performs poorly under cloud cover because of atmospheric scattering

12. Spectral reflection
The reflectance spectrum can be measured in the laboratory or in the field using a spectrometer
The spectral signature potentially varying over time (as vegetation develops or senesces) or space (field effects)
If the ratio or difference of specific reflectivities are very sensitive to plant species or health, then they can be used as a diagnostic tool

13. Remote sensing of vegetation
Large difference between % reflectance of Red and NIR light by a healthy plant
Feature that is central to remote sensing of plants

14. Normalized Difference Vegetation Index (NDVI)
Healthy green leaves:
strongly absorb red light
(i.e., low reflectance)
weakly absorb light in the NIR
(i.e., high reflectance)
Non-green vegetation or soil background is opposite
Normalized Difference Vegetation Index (NDVI)
Function of vegetation cover, biomass, leaf area index (LAI), and leaf chlorophyll concentration