ATMS 748 Homework and Course Deliverables (return to main page)
[How to write lab report]


 

Assignment 3
Short Title: Spectral surface albedo in Reno NV

The goals of this assignment are:

a. Learn how to measure surface albedo with a two spectrometer system.
b. Learn about the variability of albedo for varying land surfaces.
c. Determine the amount of solar radiation absorbed.
d. Appreciate how remote sensing can be used to determine land cover.

Surface albedo measurements for different surfaces using the two spectrometer based system.
Interpret. We have already measured surface albedo for snow as in the daily notes pages.
Measure albedo of brown and green pine needles and interpret how you would use these measurements to do satellite remote sensing of a forest to determine live and dead tree content.
Measure as many types of surfaces as possible.
Measure albedo of a dry soil surface. Then wet it and repeat the measurements.

Measurements:
a. Use the 12" x 12" teflon target backed by aluminum paint as a reference for the albedo measurements.
b. One person operates the computer, and probably needs to be shielded from the sun to be able to see the computer screen.
c. One person holds the spectrometer. Note the string with weight to identify the target, and the two bubbles to identify the instrument level.
d. One person photographs each place where measurements are obtained, and the sky conditions (clear, cloudy, etc).
e. One person takes notes of the time for each measurement, filenames, sky conditions, and any problems that are encountered.
Be sure the person managing the spectrometer faces towards the sun so that no shadow is made by the person.
f. First line up the spectrometer for the reference target measurement. Change the integration count for each spectrometer so that the measurements counts are about 3500.
g. Do the dark measurement with the two rubber pieces used to block the light. Make sure dark subtraction is done on both spectrometers.
h. Do the reference spectral measurements of downwelling irradiance and upwelling radiance (from the teflon calibration target.) Save these two files.
NOTE: Save files as text with header information. Be sure files are being saved.
i. Do the surface spectral measurements, again of downwelling spectral irradiance and upwelling radiance from the surface you are studying.
j. Measure the surface temperature using a hand held infrared thermometer.
k. Measure the air temperature to gain an understanding of the difference with temperature.

In your write up:
Choose a title that represents your findings.
Discuss the importance of surface albedo measurements, making reference to the literature.
Describe the instrument and how the measurements are made.
Compare your measurement method with others in the literature.
Describe uncertainties in the measurements.
Display your results, with a photograph for each spectrum.
Display your results of use of ImageJ to separate colors, and to estimate a Red, Green, and Blue color albedo.
Calculate the amount of solar radiation absorbed by the radiation within the spectral region of your albedo measurements. How much radiation is potentially missing from this estimate due to finite wavelength range?

Extra: Model the surface temperature for both dry and moist surfaces.


Some resources:
Presentation.
Related presentation.
Fortran program used to process the raw data (includes a nifty subroutine that generates a gnuplot script and calls it.)
Solar spectrum at top of the atmosphere.
DOE SMARTS program 'SMARTS' and simulate the radiation in the atmosphere, for use in estimating .
ImageJ software can be used to separate the 3 colors from photographs to get a quick estimate of spectral albedo.

 

 

Assignment 2
Title: Design, implement, and discuss how to use the Arduino with LEDs of various colors as light detectors (rather than as light sources).

The goals of this assignment are:

a. Reinforce the use of LEDs (and by connection, photodiodes) as light detectors.
b. Introduce a very common, and extremely useful device for measurements, the operational amplifier.
c. Show how you can get quantitative measurements from the Arduino microcontroller.
d. Learn the difference between ideal voltmeters and real voltmeters, that meter input resistance matters.

1. Build a simple circuit with a resistor and LED as a photodetector so that you can measure the photocurrent from the LED such that 0.1 microamps produces a 1 volt signal. What resistance value are you going to need to 'program' the voltage output this way?

2. Construct transimpedance amplifier circuit with an op amp to convert the photocurrent from an LED as a light detector to a voltage so that a photocurrent of 0.1 microamps produces a 1 volt signal.

3. Write a sketch for the Arduino to output relative time, and voltage from these circuits with as fast an update time at you can make.
You may need to increase the serial communication rate with the computer and write your code so that the Arduino makes efficient use of computing time .
Use a light source and rapidly shine it over the detectors.
Write your data to a file using either hyperterminal for the old computers, or another serial port capture program for other systems.
Graph your time series. Compare the time response and noise of these circuits.

4. We will do this exercise in class as a group. Here is the data we acquired on Wednesday 24 February 2016.
Use the fast ultrabright LED light source to drive both circuits at the same time with a square wave using the function generator.
Record the waveforms for both circuits simultaneously for frequencies of 10 Hz, 100 Hz, 1 kHz, 2 kHz, 10 kHz, and 100 kHz.
Record the waveforms using the oscilloscope connected to the computer.
It would be good to make sure the room lights are off if interference happens.
Discuss the effect of the circuit time constant on the ability for the detecting circuit to follow slow and fast response circuits.
Estimate the LED capacitance.
Discuss the difference in noise for each circuit.

5. Extra credit: One idea is to use the LEDs as detectors to estimate/measure cloud optical thickness.
[idea for additional project: measure the downwelling solar irradiance with both blue and red LEDs.
On a clear day the blue channel should receive more radiation than red compared with a cloudy day.

Assignment 1

Do all 12 projects in the Arduino guide book.
I strongly recommend you install the Arduino software on your own laptop, and use it in class, if you have one.
The code for the projects is here: expand the file and put the folder in your Arduino examples folder.

Write a report about 3 of the experiments, temperature measurement, light measurement, and shift register control of 8 LEDs.
Your report needs to include the following (and see below for general reporting requirements):
What is the Arduino?
What is the principle of operation of the temperature sensor? How was its signal obtained?
What is the principle of operation of the light sensor? How was its signal obtained?
What is a shift register? How and why are they used?

Final open ended question: What would you like to do with the Arduino and appropriate hardware (you specify), if given the time and resources for development?

EXPECTATIONS IN LAB REPORTS

Lab reports will be written the same format we use for scientific papers and for student senior, MS, and PhD theses.
One goal of this class is to work on your ability as a science writer.
Let me emphasize one word here. SCIENCE SCIENCE SCIENCE SCIENCE SCIENCE SCIENCE!!!!
So often we are obsessed with the technical details of the measurements that we don't cover the science adequately.
The following elements are needed for your lab report to be complete.
Here is an example of some hints I found using a google search with the keyword "how to write a scientific paper".
Page length doesn't matter; it's all about the contents.
Make it as short as possible to get the message across in a clear manner.

Title: The title should cover the science objective and maybe mention the instrument(s) used for the measurement.

Abstract: The abstract is a brief discussion of the findings of your work. It should be well written because it is often what is read as someone makes a decision to read your work (or fund your research).
Hint on writing abstracts.

Introduction: Explain the scientific goal in more detail and maybe hint at the measurement methods used.

Measurements: Discuss the measurement methods, including uncertainties.
Discuss the instrument(s) and the pertinent information needed to convey what you measured.

Observations: Display your observations and interpret them for your reader.
Make clear, legible graphs with large fonts, clear symbols, and clearly documented results.

Conclusions: The conclusion should summarize your observations and perhaps make suggestions for future work.

References: References refer to specific articles and/or books, etc, that you reference in your paper.

HERE IS AN EXAMPLE LAB REPORT

 

 

 




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