Hands On Physics

Haze
Photometer Notes

Using the VHS

  • You can use the Sun Photometer to find out how the AOT changes over a day, week, season or even an entire year. If you follow the instructions in this manual and use care in making your measurements, the data you collect will have important scientific value. Therefore, you might want to consider using the Sun Photometer in a serious science fair project or just a long-term environmental monitoring project. You can even exchange data with other students via the Internet to find out how haze changes in other regions.

  • Here are some important operator tips:
  • WARNING: ALWAYS WEAR SUNGLASSES WHEN LOOKING AT THE SKY! NEVER LOOK DIRECTLY AT THE SUN EVEN WHEN WEARING SUNGLASSES! Looking at the Sun may cause temporary or even permanent damage to your vision.

  • If you want to study the AOT over time, try to make your measurement at about the same time every day. Good choices are mid-morning, noon and mid-afternoon. If you make three or more measurements during the day, you will be able to see the changes that often occur as the day warms or when the weather changes.

  • Always enter in your notebook the date, time of measurement, dark signal, Sun signal and sky condition at the time of the measurement. It's especially important to describe any clouds or cloud haze in the vicinity of the Sun that might increase the AOT.

  • If you can't take your notebook with you for some reason, stick a removable label on the Sun Photometer before you go out to measure the Sun. You can write the time and the measurements on the label for transfer to your notebook.

  • Try to process your data to recover the AOT as soon as you can. If the AOT is especially low or high, you may want to make more measurements.

  • Use graph paper or a computer to make a running graph (known as a time series) of your AOT measurements from about the same time every day.

  • Always save your raw data (date, time, dark signal and sunlight signal). TERC plans to carefully test and evaluate the various formulas and spreadsheets used to convert your readings into AOT. Should we find ways to improve the formulas, we will publish them so you can update your results.

  • Finally, store your notebook in a safe place and backup any data you enter into a computer! You have worked hard to obtain your data, and you don't want to lose it! If you are a careful Sun photometer user, your data will provide a very important addition to knowledge about haze in your area. It is quite possible that other students and even professional scientists will want to study your data.

    • Maintaining the Sun Photometer

    Here are some important tips for maintaining the Sun Photometer:
  • Store the instrument inside a sealed plastic bag to keep dust away from the LED sunlight detector.

  • The black plastic of the Sun Photometer case will quickly warm up in exposed sunlight. Since the light response of the LED changes slightly with temperature, keep the instrument covered or inside a backpack or box until just before you plan to use it.

  • NEVER leave the Sun Photometer in exposed sunlight.

  • NEVER leave the Sun Photometer inside a car or car trunk on a hot, sunny day.

  • The batteries should last a full year or more in normal use--unless you forget to switch the instrument off when it is not in use. If the instrument seems erratic or doesn't respond well to sunlight, use the voltmeter to check the battery voltages. Replace the batteries when their voltage falls below about 7 volts.

  • You should check the calibration of the Sun Photometer using the Langley method on at least one clear day every fall and spring. Keep a careful record of your calibrations to determine how much the ET constant changes.

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