What is the units of reflectance used in remote sensing?
Reflectance is the ratio of the amount of light leaving a target to the amount of light striking the target. It has no units.
How is spectral reflectance measured?
Reflectance is measured by shining light on a sample and measuring the light reflected from the sample. Reflected light consists of specular reflected light and diffuse reflected light, which when combined together is referred to as total reflected light (specular reflected light plus diffuse reflected light).
What is SR in remote sensing?
Definition. Remote Sensing Reflectance, Rrs(λ; sr-1), is water-leaving radiance, Lw(λ), corrected for bidirectional effects of the air-sea interface and sub-surface light field, and normalized by downwelling solar irradiance, Ed(λ), just above the sea surface.
What is TOA reflectance?
Top-of-atmosphere reflectance (or TOA reflectance) is the reflectance measured by a space-based sensor flying higher than the earth’s atmosphere. These reflectance values will include contributions from clouds and atmospheric aerosols and gases. Surface Reflectance.
What are the units of spectral radiance?
For radiation power per unit of wavelength, spectral radiant flux is used with SI units of watts per meter [W/m], or more commonly milliwatts per nanometer [mW/nm]. For radiation incident on a surface, the term spectral irradiance is used, and has the SI unit of [W/m3], or more commonly units of [mW/mm2-nm].
How is mirror reflectivity measured?
The Solution: Cavity Ring Down Spectroscopy (CRDS) A detector placed after the second mirror measures the decreasing intensity of the reflected light. The total loss of the mirrors is determined by the decay time, or “ring down”, of the reflected light.
How do you calculate surface reflectance?
Reflectivity can be calculated as p(y) = Gr(y)/Gi(y) where p is the reflectivity, y is the wavelength of the light, Gr is the reflected radiation and Gi is the incident radiation. Calculate reflectance from the reflectivity. Reflectance is the square of the reflectivity so q(y) = (Gr(y)/Gi(y))^2.
What is nitrogen reflectance index?
Bausch and Duke (1996) proposed a vegetation index called the nitrogen reflectance index (NRI). The index requires a relationship for each growth stage since it was normalised to a reference representing an area where there is no N stress.
How do you calculate reflectance value?
What are the units of radiance?
The SI unit of radiance is watts per square meter per steradian [W/m2-sr]. Since many radiation sources used in laboratories have emitting area in the square millimeters range, the unit of milliwatts per square millimeter per steradian [mW/mm2-sr] is often used for radiance.
What unit is radiance measured in?
watts per square meter per steradian
The SI unit of radiance is watts per square meter per steradian [W/m2-sr]. Since many radiation sources used in laboratories have emitting area in the square millimeters range, the unit of milliwatts per square millimeter per steradian [mW/mm2-sr] is often used for radiance.
What is the unit of radiant flux?
The SI unit of radiant flux is the watt (W), one joule per second (J/s), while that of spectral flux in frequency is the watt per hertz (W/Hz) and that of spectral flux in wavelength is the watt per metre (W/m)—commonly the watt per nanometre (W/nm).
What is the unit of reflection?
Radiant intensity per unit frequency or wavelength. The latter is commonly measured in W⋅sr−1⋅nm−1. This is a directional quantity. Radiant flux emitted, reflected, transmitted or received by a surface, per unit solid angle per unit projected area.
What is percent reflectance?
Reflectance (R) is the amount of reflected radiation over the amount of. incoming radiation power. 2. Absorption (A) is the amount of absorbed radiation over the amount of. incoming radiation power.
What is the reflectance of a mirror?
Properties of a Mirror Figure 1: Reflection of light on a mirror. The reflectivity (or reflectance) is the percentage of the optical power which is reflected. Generally, it depends on the wavelength and the angle of incidence, for non-normal incidence often also on the polarization direction.
How do you calculate average reflectance?
The weighted average of reflectance over the entire room surfaces, ρ′, can be expressed as follows:(2) ρ ‘ = ρ wall · A wall + ρ ceiling · A ceiling + ρ floor · A floor + ρ window · A window A where Awall, Aceiling, Afloor, and Awindow represent the surface area of wall (window area excluded), ceiling, floor, and …
What is surface reflectance?
Surface reflectance is the amount of light reflected by the surface of the Earth. It is a ratio of surface radiance to surface irradiance, and as such is unitless, with values between 0 and 1.
How do you measure nitrogen in plants?
By using spectroradiometers, reflectometers, imagery from satellite sensors and digital cameras, optical properties have been measured to estimate N in plants, such as crop canopy reflectance, leaf transmittance, chlorophyll and polyphenol fluorescence.
Is reflectance a good unit of measure for remote sensing?
Although reflectance is a key unit of measure in remote sensing, it is not measured directly and instead must be derived.
Is remote sensing reflectance the key to ocean color retrieval?
Spectral remote-sensing reflectance ( Rrs, sr −1) is the key for ocean color retrieval of water bio-optical properties. Since Rrs from in situ and satellite systems are subject to errors or artifacts, assessment of the quality of Rrs data is critical.
What is the difference between reflectance and radiance?
Unlike radiance and irradiance values, reflectance is an inherent property of an object and is independent of time, location, illumination intensity, atmospheric conditions and weather. Although reflectance is a key unit of measure in remote sensing, it is not measured directly and instead must be derived.
How can I use reflectance data as a source of information?
Field or laboratory reflectance data can also provide a sole source of information (independent of remote sensing imagery), such as with surface target identification using pattern search and matching techniques with known reflectance curves from established spectral libraries.