To help evaluate the complexity of this experiment, below you will find a basic list of instructions.

Procedure (List of steps only)

1. Determine latitude and longitude for your geographic location.
2. Prepare the inclinometer to measure Sun angle.
3. Attach the Sun photometer to the voltmeter and turn both instruments to the ON position
4. Record the time of day, the temperature, the barometric pressure, and the sky conditions.
5. Measure and record the Sun angle
6. Record the dark voltage
7. Record the Sun signal
8. Enter data into algorithm to determine the Aerosol Optical Thickness (AOT).

Procedure with explanation

1. Determine latitude and longitude for your geographic location.

   The location of any point on the Earth's surface can be uniquely specified by its latitude and longitude. An imaginary line circling the Earth in a north and south direction is called a meridian line or a longitudinal line. There are an infinite number of these imaginary meridian lines circling the Earth. Each line traces a different path around the Earth, but they all intersect at each of the poles. Each meridian line is specified by the angle at which it intersects with a selected reference meridian line. The universally accepted reference meridian passes through Greenwich England, and is defined as the zero meridian. Every other meridian line is specified by the angle between it and the zero meridian, and its direction east or west of the zero meridian. For example, Hampton, Virginia is west of the zero meridian, and the angle between meridian line passing through Hampton and the zero meridian is approximately 76°. Thus, we say that Hampton is located on the 76° west meridian.

   There are also an infinite number of imaginary lines that circle the Earth in the east and west direction. They are called latitudinal lines or parallel lines because they are parallel to each other. Like the meridian lines, each parallel line traces a different path around the Earth. The equator is one of these lines. Each parallel line is specified by its angle north or south of the equator. Using Hampton, Virginia as an example again, the parallel line passing through Hampton is approximately 37° north of the equator. So, the 37° north parallel line (37° N Latitude) and the 76° west meridian line (76° W Longitude) intersect at Hampton, Virginia. Hampton's location on the Earth is therefore specified by the point; 37°N, 76° W. The latitude and longitude can be determined for any place in the world by locating the place on the world atlas (in most libraries) and finding the latitudinal and longitudinal lines that intersect at that place. The latitude and longitude of many cities around the world can be found on the National Weather Service web page. The latitude and longitude of locations in the United States can be found at the Cenus Bureau web page.

2. Prepare the inclinometer to measure Sun angle.

   The inclinometer is a device for measuring the angle between the horizon and the Sun.

   The Sun angle is the angle between the horizon and the Sun. It is measured to the nearest half degree.

3. Attach the Sun photometer to the voltmeter and turn both instruments to the ON position

   The Sun photometer is the instrument used to measure the intensity of direct sunlight.

   The voltmeter is used to measure voltage in an electrical circuit. Check to see if the voltmeter is correctly connected to the Sun photometer. The voltmeter should have a small positive reading or a reading of zero when turned on.

4. Record the time of day, the temperature, the barometric pressure, and the sky conditions.

   Record the local time of day in 24-hour format, and then convert this reading to universal time.

   Record the temperature to the nearest degree expressed in Celsius degrees. If you are taking measurements with a Fahrenheit thermometer, you must convert this measurement into Celsius degrees

   Using a conversion formula: C = 5/9(F -32)

   Example:

   Problem: Convert 75°F into Celsius scale

   Solution:

   C = 5/9(F - 32)

   C = 5/9 (75 - 32)

   C =24°

   Using a conversion table or calculator program

   Barometric Pressure is the measure of how much pressure the atmosphere is exerting on the surface of Earth.

   It can be measured in inches of Mercury (inHg) or in hectopascals (hPa).

   To determine barometric pressure, you may use a barometer or obtain the information from a web page such as the Weather Channel or your local newspaper.

   If you do not have a barometer or cannot determine the barometric pressure from other sources, use the standard pressure. Standard pressure is 1013 hPa or 30 inHg.

   Use the scale below to determine a rating for the sky conditions.

   Ratings for sky conditions
   What to observe	1	2	3	4	5
   Cloud covering	Overcast skies or precipitation	Mostly cloudy	Partly cloudy	Mostly clear sky or very light clouds	Clear sky with no clouds
   Presence of shadows	No shadows visible	Poorly defined shadows	Mostly well-defined shadows	Well-defined shadows	Very clearly-defined shadows

5. Measure and record the Sun angle.

   The Sun angle is the angle between the horizon and the Sun. Measure the Sun angle using the inclinometer or the shadow method.

6. Record the dark signal.

   The dark signal is the voltage reading on the voltmeter when no light is coming through the Sun port.

   To find the dark signal: Go outside to the location of data collection. With the Sun photometer and the voltmeter in the ON position, cover the Sun port snugly with one finger so that the Sun's light is not entering the Sun photometer case. The voltmeter reading in this position is called the Dark Signal.

7. Record the Sun signal.

   The Sun signal is the voltage reading when direct sunlight is entering the instrument through the Sun port.

   To find the Sun signal: Go outside to the location of data collection. With both the voltmeter and the Sun photometer in the ON position, aim the Sun port of the Sun photometer at the Sun so that the Sun's light is entering the instrument and the Sun spot is hitting the Sun target pre-marked on the side bracket.The voltmeter reading in this position is called the Sun signal.

8. Enter data into algorithm to determine the Aerosol Optical Thickness (AOT).

   An algorithm is a mathematical equation.

   SAGE III scientists have developed special mathematical equations for use in processing the data from the SAGE III instruments.

   An algorithm is also used to process the students' data from their hand-held Sun photometers. The data collected is entered into a mathematical equation to determine the Aerosol Optical Thickness of the atmosphere at the time of observation.

   Atmospheric Optical Thickness is a number which expresses how difficult it is for light to pass through the atmosphere. A small number would mean that light could pass through the atmosphere fairly easily. A higher number would mean light is being blocked or scattered by a larger amount of clouds, aerosols, and gases, and is having difficulty passing through the atmosphere.

   If scientist need to know specifically how difficult it is for light to pass through only the aerosols in the atmosphere, they will use an algorithm to determine the Aerosol Optical Thickness (AOT). This algorithm accounts for the Rayleigh Scattering so that it does not effect the value of aerosol measurement.

   The algorithm used to find Aerosol Optical Thickness is
   
   

   AOT	=	ET constant - ln(Vs - Vd) -(0.117M)(P/1013.25) M

   
   
   Where AOT = Aerosol Optical Thickness
   ET constant = Extraterrestrial constant for the instrument
   Vs = Sun signal (volts)
   Vd = Dark signal (volts)
   M = Air mass
   P = Barometric pressure (hPa)

   To calculate the Aerosol Optical Thickness (AOT) for a set of collected data, substitute the observed values for the variables in the algorithm. Complete the calculations (using a scientific calculator). The resulting answer is the AOT value for that particular collection location, date, and time.