Science Buddies: "Ask an Expert"

Congratulations! I'm happy for you.

Hi Chris,
I do not understand this data that Gaby posted:
7. Home- 2
· Date= Jan. 17, 2007
· Time= 2:54 pm
· Temperature= 33° F
· Pressure= 30.72"
· Weather= clear
· Dark signal= 0.288v
· Sun signal= 3.74v
· Altitude angle= 26.47°
· Relative air mass= 2.244
· Ln signal= 1.239
· AOT= 0.041

It should be negative AOT, right ?

In any case, I am getting all AOTs negative, please help me understand this:

few examples:
Sun angle : 16.89,
Pressure (in inches): 30.33
Sun signal : 2.2v [ dark - sun ]
Airmass calculated : 3.44
MY ET : 1.78
AOT as -0.180.
=============
Sun angle : 29.85
Pressure (in inches): 30.30
Sun signal : 3.02v [ dark - sun ]
Airmass calculated : 2.01
MY ET : 1.78
AOT as -0.280
=============


Is it wrong ?

Thanks,
nxg

Hi nxg,
I also got different AOT values from Gabby's measurements.

For your first set of measurements, I calculated the same AOT as you. On the second set, I calculated an AOT of -0.38.

As far as an explanation for why your values are all negative, one possibility is that there is a problem with your ET value. For the first set of measurements, you would need an ET > 3.4 to bring your AOT into the positive range. I would suggest calibrating the instrument again, which is never a bad idea, even if your results seem reasonable. I do not think the m values are the culprit here - no matter how I change those, the AOT remains negative.

I hope that helps.

Chris

Hi Chris,
I think I know where the problem is. The graphical method of finding out ET gives me ln(ET), not ET, right ? If that is the case, then I am getting AOT as about 0.16 all the time. So, my ln(ET) was 1.78. Not ET.

I have to turn in the project in two days. I am assuming that anyways.

Thank you very much for your help. I really appreciate it.

nxg,
I believe you are correct. Congrats on figuring that out, and good luck with the final work on your project. It sounds like it will be very impressive.

Glad to help,
Chris

Finally I am ready with the project [ tomorrow] presentation and stuck with the following question. If AOT is the measurement of Haze why is this supposed to be fixed ?

Thanks,
NxG

Hi nxg,
I'm not sure I understand your question. Does it say somewhere that AOT should be constant?
Chris

Hi Chris,
While reading some part from haze101 -- I came across somewhere that AOT will be same, that's what confused me. Now, I did little more research and my confusion is clear.

Thanks,
NxG

OK. Good luck with your presentation!

now that i think about it i wanted to talk to you about the results i got when i measured the haze and did the formula. i was jsut wondering if i did everything right.

Hi Chris,
Thank you very much for your help. It went well, waiting for my grades.

Thanks,
NxG

Nxg, I'm glad to hear it! I hope you will get the grades that you want.

Gabby,
I think that you did your calculations correctly. I believe that nxg and I were originally getting different results from you because there was some confusion about ln(ET) versus ET. Now that the confusion is cleared up, I rechecked one of your calculations and got the same result. Good for you for following up on the work!

YAY!!! thankyou soooo much! ok well ill do the project again next year so i can get more data sooo until then BYE!!!

That's a good idea - now that you've done the hard work of building the equipment and figuring out the calculations, you'll be able to spend more time planning the experiment and collecting data.
See you next year.