LABORATORY: ATMOSPHERIC ATTENUATION OF SOLAR RADIATION

Objective:

The  molecular  and  aerosol  constituents  of  the  earth's  atmosphere  cause  scattering  and absorption  of  the  incident  solar  radiation  altering  the  spectral  character  of  the  irradiance reaching  the  surface  as well  as generating  scattered  light  into  the  space borne or  airborne sensor.  Although  the  characteristics  (brightness  and  spectral  distribution)  of  the  solar radiation outside the earth's atmosphere (known as the exo-atmospheric solar irradiance) has been measured repeatedly and is considered well-known, the characteristics of the radiation field received at the earth's surface is highly variable, dependent primarily on the solar angle and  the optical properties of  the atmosphere. The objective of this lab is to expose you to methods measuring the direct and diffuse spectral irradiance received at the surface as well as the extinction of the solar beam by the atmosphere.

Assignment -

The practical purpose of this experiment is to familiarize you with the analysis of data from a sun photometer to derive atmospheric optical properties.

Sample SONOTEK data previously acquired by your TA is provided so you can get some experience in its analysis.

1) Using the solar ephemeris spread sheet program (ESSE 4220_EPHEMERIS) provided, calculate the solar zenith angle and the corrected air mass for each measurement time and tabulate the values, and submit these in a form as shown in Table 1.

2) Produce a Langley plot. For  each  channel  and derive  the  corresponding  zero  air-mass Calibration constants S_TOA;λ for the sun photometer. Correct these values to the mean-earth- sun distance values to determine the standard calibration constants S_o(λ) for this. Enter these results in Table2. 

3) The Langley plot analysis also yields  the  total optical depth of  the atmosphere on  the day of measurements. Calculate  the aerosol optical depth at each wavelength for each of  the measurement times and compute the Angstrom exponent. Enter your results in Table2.

Attachment:- Assignment Files.rar