# Presentation: 489451

## A Dictionary of Remote Sensing Terms

- Richard Kleidman
- SSAI/NASA Goddard
- Lorraine Remer
- NASA Goddard

## Let’s look at 3 kinds of properties that are 

- important to understand about aerosols
- Chemical Properties

- Physical Properties
- Optical Properties

- Because we measure the entire column our properties
- represent the mean particle characteristics

## Physical Properties

- Aerosol Amount

- AOD - Aerosol Optical Depth
- AOT - Aerosol Optical Thickness
- These optical measurements of light extinction
- are used to represent aerosol amount in the entire
- column of the atmosphere.

## Slide 4

## Physical Properties

- Aerosol Amount - AOT, AOT

- Aerosol Mass Concentration - Mass / cm2 (MODIS Units)
- PM 2.5 - particles of less than 2.5 μm aerodynamic diameter
-   These can penetrate deeply into the lungs
-  PM 2.5  concentration at ground level is an important parameter for air quality studies.
- CCN (Cloud Condensation Nuclei) Concentration.
- These are particles that act as condensation surfaces and
- encourage water droplet formation within clouds.

## Physical Properties

- Particle Size Distribution -  There is an assumption,
- based on many years of measurements, that aerosols
- in the optically active size ranges are best represented
- as a bimodal distribution.  The aerosol size distribution
- can be represented as a volume or number distribution.
- The mode representing the small (fine mode) aerosol
- has a size distribution centered on radii between
- 0.1 and 0.25 microns.
- The mode representing the large (coarse mode) aerosol
- has a size distribution centered on radii between
- 1 and 2.5 microns.

## Size Distribution

*dV* / *d*ln*r*

- Radius , *r,* (m)

- “coarse” mode

- “fine” mode

- Approximately
- “lognormal” shape

## Physical Properties

- Angstrom Exponent
- The Angstrom exponent is often used as a qualitative
- indicator of aerosol particle size, with values greater
- than 2 indicating small particles associated with
- combustion byproducts, and values less than 1
- indicating large particles like sea salt and dust.

- For measurements of optical thickness
- 1 and 2 taken at two different wavelengths 1 and 21

## Physical Properties

- Particle shape - spherical, spheroid, non-spherical

## Optical Properties

- Single Scattering Albedo - a measure of how absorbing
- or scattering we consider the mass of aerosol particles.

-                       AOTscatter
-   o     =   _________________________________
-              AOTscatter   + AOTabsorption

- Values of .85 are considered very absorbing
- Values of .95 are considered very non-absorbing

- Extinction = Scattering + Absorption

## Optical Properties

- Scattering Phase Function

- The directional light scattering
- due to the aerosol particles

## Optical Properties

- Sample Phase Functions

## Optical Properties

- Complex Index of Refraction

- Real Component - refers to light bending

- Imaginary Component - refers to light absorption due
- to the material

## Radiative Transfer

-     The physics and mathematics of how radiation passes through a medium that may contain any combination of scatterers, absorbers, and emitters.

## Aerosol Inversion

- Using the measured optical properties
- to infer the physical characteristics of the
- Aerosol.
- This is performed by an inversion of the
- Radiative transfer equations.