ATMS 749 Radiation Transfer Notes [MOST RECENT NOTES] [Main Page] [Homework]

General
Wood smoke optics as affected by RH.
Multispectral measurements of wood smoke optics.
Condensed version of the two above talks, given at DRI on 27 Sept 06 by Kristin Lewis and me.
Photoacoustic measurements of aerosol light absorption.
Pictures taken by students.
Mexico City Aerosol Optics talk, given at UNR on 9 Oct 06 by Lupita Paredes and me.
Second Mexico City talk with meteorology for the student AMS chapter, 9 Nov 06, by Lupita Paredes.

Chapter 1 (and other topics) Emission, the Birth of Photons
1st Class Meeting 8/29/06 Blackbody radiation, distribution functions, and UV radiation.
2nd Class Meeting 8/31/06 Emissivity of minerals, gases, water surface, and angle dependence of emissivity.
3rd Class Meeting 5 Sep 06 Snell's Law, Fresnel Reflection Coefficient, Electromagnetic Theory.
4th Class Meeting 7 Sep 06 Blackbody radiation, Brightness Temperature, theoretical spectra for gases.
5th and 6th Class Meeting 12 and 14 Sep 06 Brightness temperature and absorption of IR by the body. Climate.
7th Class Meeting 19 Sep 06 Climate and climate change. Greenhouse gases are a good thing, too much of a good thing gives a fever.

Chapter 2 Absorption, the Death of Photons
(Alternative, simpler point of view, good primer to read perhaps before Bohren's chapter 2.)
Notes on Chapter 2 topics, discussed 21, 26, 28 Sep 06, some notes from Grant Petty's book.

26 Sep 06 9th Class Meeting Cross Sections discussion, basics.

3 Oct 06, summary of chapter 2.Take home message as cartoons for emission/absorption spectra.

5 Oct 06 Thursday, My notes on the Schwarzchild equation, and related presentation showing examples of FTIR Spectra. See also Chapter 8 of Petty on the subject, for reference, and for assistance with the homework. This is the formal presentation of radiation transfer in the IR when scattering is negligible, and the examples are very practical consequences of this relatively simple theory.

10-12 Oct 06 Tuesday, My notes on application of the Schwarzchild equation to explain the Schnauzer FTIR spectra. See also Chapter 8 of Petty on the subject. Also will discuss the temperature dependence of spectral line strength and width. Also will consider absorption of solar radiation (UV and Visible). See also the notes by Liou on this subject. Also continue with the presentation for IR spectra, and solar absorption.

ASIDE: Consider WIMPS: Weakly interacting massive particles, they comprise 75% of the universe, in theory, though haven't been proven to exist in reality. They interact with matter only through the weak nuclear force and gravity. Their concentration is around 1000/m^3. They travel at 220 km/sec. Their mass is 100x the proton. Their cross section for interaction with atoms is 10^(-42) cm^2. WIMPS see protons in matter via the weak nuclear force -> so the cross sections for interaction with protons should be much larger when matter is very dense and hot so that protons are in nuclear states that interact well with WIMPs, in analogy to the way that atmospheric infrared cross sections for absorption depend on the thermally driven energy level populations. See my notes on how to calculate the number of WIMPS passing through your head right now, how many are in it at any time, and how long you have to wait until one is absorbed by a proton in your head.

12-17-19 Oct 06 , See my notes on the use of Anomalous Diffraction theory to calculate particle cross sections and cirrus cloud emissivity in the zero scattering approximation. This theory is used to explain the observed FTIR brightness temperature for small crystals in cirrus as given in the revised presentation that also contains introduction to light scattering by particles. and in a related spreadsheet.

Also see my notes on the introduction to multiple scattering, the formal theory. We set up the framework and identify the important parameters that need to be clarified with respect to optical properties of single particles and gases. See also Chapter 11 of Grant Petty on the radiative transfer equation with scattering.

We will then go into the multiple scattering theory, approximated in 1 dimension, using the very insightful paper by Craig Bohren.

Chapter 3 Scattering, the Life of Photons
Read Chapter 12 from Grant Petty on the same subject.
Some basic ideas in geometrical optics applied to particle scattering, from Petty.
Bohren's Book, Best Selections to Read:
Section 3.2 Scattering by a Dipole.
Section 3.4.2 pg 136, etc, Coherence.
Section 3.4.6 pg 143, etc, The Doppler Effect, in particular, know how to use Eqs. 3.73 and 3.74, and read carefully the paragraph "Doppler radar..." near the bottom of pg 146.
Pg 154, Frequency dependence of scattering by air molecules.
Section 3.5 Scattering by particles, pg 154-175.

24 Oct 06 Presentation by Kristin Lewis on the optical properties of woodsmoke as measured in the laboratory.
Homework: Study the online learning presentation that discusses how dust is detected from satellite imagery. Write a paragraph each summarizing what you learned from each presentation.

Results: A nice summary of the presentation and satellite imagery.

26 Oct 06
HOMEWORK CLASS PREPARATION:
Study the introduction followed by in depth discussion microwave remote sensing using satellites (COMET MODULES).

IN CLASS, AS A CLASS AS HOMEWORK TO BE TURNED IN AS A COLLECTIVE: This spreadsheet uses the zero-scattering approximation method to calculate FTIR spectra for cirrus containing small ice crystals. In class, write out the equations on the board for this model, where cirrus emissivity is calculated using the simple anomalous diffraction theory. Play with the parameters in the model, in the spreadsheet, to see what effect they have on the brightness temperature (larger/smaller cloud length, higher/lower crystal concentrations, larger/smaller particles, larger/smaller cirrus temperatures). See if you can get the model to produce a better fit with the observations. Have one person report the findings in a written report that contains also the names of people present (so the collective homework can be graded.) Also sketch out the theory in detail so that you could give it to someone else to calculate it. Then find at least 5 ways to criticize this model, and add them to the written report.

Results: The written report does a good job of working this problem, and I made a few additional comments.

2 Nov 06
Discussed UV photons in the atmosphere a bit more, with regard to formation of oxygen singlet D and HO and its role in chemistry.
Spent most of the time carefully discussing the nature and equations for electromagnetic scattering by dipoles in the atmosphere. Notes were from Liou.
References: A site on Rayleigh and Mie scattering.

7 Nov 06
Rayleigh scattering notes from Liou. It would be good to print these out and study them.
Rayleigh scattering presentation, and especially the connections with UV radiation in the atmosphere.
(Much of this presentation was derived from spreadsheet calculations of Rayleigh scattering by air.)
We looked at a demonstration of Rayleigh scattering by small fat particles in a glass of water, and the polarization dependence of this.

9 Nov 06
We are transitioning between single particle scattering properties (Petty's Ch12 is a good source, and will be discussed in class, good to print out and bring to class for additional note taking ) to multiple scattering (Bohren's excellent paper).
Today's lecture covered the general formulism for multiple scattering and the beginning of the reduction of this theory to 1-D for the 2 stream model. Chapter 11 of Petty is a very good source for this lecture.
References:
Particle scattering and absorption are measured at background sites by NOAA CMDL.
Check out the glory!
Check out the rainbow!
Check out radar cross sections for chaff!
Atmospheric Chemistry and UV photons (diagram of O OH) (Atmospheric Chemistry) (Double conjugated bonds and light absorption)

14 Nov 06
Midterm notes and the midterm are posted here and on the homework page.
Time to read Bohren's excellent paper on multiple scattering in earnest. Also, follow up by reading chapter 5 in Bohren and Clouthiux's text . We will work through the paper, and then link it back to the text for some applications.
We must intersperse a bit more single scattering as well...
Calculate scattering properties of spheres, online.
Using CH12 of Petty, look at...
Rayleigh scattering, its dependence on wavelength and particle diameter.
The first few terms of the Mie theory, scattering and extinction for very small particles.
The phase function as a function of size parameter, to see the rainbow and glory, and the small particle limit.

16 Nov 06
Aside: Some water optical properties.
Tabulated absorption in the visible.
Tabulated absorption UV to IR.
See also other wavelength ranges.
Absorption and penetration depth plot.
Spectral transmission plot as a function of depth.

Homework 7 on multiple scattering has been posted. We will continue to develop the consequences of multiple scattering on transmission and reflection of light through optically dense media. The same references as discussed on the 14th should be used again. We will look again at dipole scattering by small particles suspended in water, but will complete the transition to multiple scattering.

21 - 5 Dec 06
Continue with the multiple scattering model in 1 D development.
Midterm notes and the midterm are posted here and on the homework page, and compare the last problem, heating rate due to black carbon, with heating rates for gases in the atmosphere. See also Petty's discussion of heating rates.
30 Nov 06 Direct, diffuse and total radiation from the 1-D, 2 Stream model for radiation. (Reminder from sites around the world, and Babs, Bsca values for aerosol.)
Eventual new topic: Laser heated particles. (A heavy version is also available.)
Ozone and NO2 absorption in the visible and near UV, details for O3 and NO2, and the combo.
Sunsets on the semester. Forecast for the final.

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