Calitoo Corner #2: "What do the values on the Calitoo screen mean?"


Today we will get a closer at look at the values displayed on our Calitoo screen.

When you first turn on your Calitoo, you will get a screen like the following: note the serial number of your instrument will be displayed. 








After the initial screen, your instrument will display basic information as shown on the following picture (Source:

TIP: The temperature displayed by your Calitoo is actually the temperature inside the instrument.

When you report data back to GLOBE, you will use the Barometric Pressure and Temperature from your atmospheric site. You may use the values reported by your local weather station. Avoid entering the temperature read by a smart phone.

After pressing the button, your instrument will display the “Maximum Measurements” screen. The photometer measures a voltage value that is proportional to the sunlight intensity sensed by its LEDs. You will see a maximum value for each wavelength (Blue, Green and Red) on the right, and the raw values fluctuating on the left, as you point the instrument to maximize such values.

The voltage value for each wavelength will then be converted to an Aerosol Optical Thickness value; the higher the voltage, the more sunlight is getting to our instrument = fewer aerosol particles scattering sunlight, expressed as a smaller AOT value.


If you are curious about the math behind converting voltage values to AOT values, please refer to Appendix 4.1 “Optical Thickness Calculation” on the Calitoo User Manual, at:

The final screen when you are on Measuring Mode, shown on the following picture, (Source:, refers to how large or small the aerosol particles are.

You will see an Angstrom coefficient, this number is inversely related to the average particle size of the aerosol particles: the higher the Angstrom coefficient, the smaller the particles. 

If you are interested in the math behind calculating the Armstrong coefficient, please refer to Appendix 4.2 “Particle characterization” on the Calitoo User Manual, at:

Please stay tuned for our next Calitoo Corner post! And remember, if you have a question or a tip to share, contact Dr. Pippin at!



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