University of Bremen IUP DOAS


DOAS HOME
NEWS
PUBLICATIONS
POSTER GALLERY
EDUCATION
SEMINAR
MEMBERS
MEETINGS
LINKS

Research

PROJECTS
SATELLITE
GROUND-BASED
AIRBORNE
DATA PRODUCTS

Navigate

Up
DOAS Introduction
MAXDOAS
Airmass Factors
DOAS Glossary
Lecture Material
City of Science
COSPAR 2010

Airmass Factor Calculator


The column retrieved from a DOAS measurement depends on the amount of the absorber present, but also on the light path through the atmosphere. The latter depends on many factors including viewing geometry and the vertical distribution of the absorber. Usually, the effect of light path is expressed as airmass factor (AMF) which is defined as the ratio between the retrieved slant column (SC) and the atmospheric vertical column (VC): AMF = SC / VC.

For overhead sun and a nadir viewing instrument, an airmass factor of 2 would result if all photons coming from the sun pass through the absorber, are reflected on the ground and travel back through the absorber to the instrument. In the same geometrical approximation, the light path at 30 solar zenith angle (SZA) would be 1 + 1 / cos(30).

In the real atmosphere, many photons are scattered and depending on surface albedo, solar zenith angle and wavelength, the sensitivity of the measurement and thus the airmass factor can deviate significantly from the geometrical approximation.

Below you can interactively change some of the parameters (albedo, layer altitude, and wavelength) and see how the airmass factor changes. You will have to enable JavaScript to run this form.

  Albedo
Wavelength

The airmass factors have been computed with the radiative transfer model SCIATRAN using the following settings:

  • Rayleigh atmosphere (no aerosols)
  • full multiple scattering
  • with refraction
  • spherical atmosphere
  • no clouds
  • US standard atmosphere

The presence of aerosols might change the results significantly by enhancing visibility in and above the aerosol layer and decreasing sensitivity below. The same is true for clouds, only much more so.

JavaScipt Slider Control courtesy of BlueShoes.

web master:  folkard@iup.physik.uni-bremen.de      Last Update: 11-04-16