| Question on collection change - MOD07 air profile [message #55157] |
Thu, 02 August 2007 23:29  |
kim20026
Messages: 54
Registered: November 2006
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Member |
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Goodday, Everyone...
I don't know this is a good place to ask my questions, but I had
already sent several e-mails to someone in Wisconsin (i.e: Dr. Suzanne
Seemann and Dr. Paul Menzel) since last week. None of them didn't
reply to us yet. They must be very busy thesedays. I feel like I am
'grabbing a floating straw to get out of a swamp!'
Our research team is currently studying on several meteorological and
ecological topics with various MODIS products. At this point, we are
trying to compare MOD07-retrieved air temperatures with those measured
from 72 locations of national weather stations in Korea.
To do this, we have used MOD07 collection 4, but recently we found
MOD07 collection 5 have been already provided. Now I have two
questions.
1. We checked the images shown in MODIS official website and compared
collection 4 image with collection 5 image at the same day. We found
air temperature at near-surface level (i.e. 20th band) mostly appeared
on the land part of the collection 4 image. However, Air temperature
at near-surface level was black out in the collection 5 image. We are
very curious about this phenomenon. Why is it?
2. MOD07 provides 20 bands. If I understand correctly, 20th band is
the nearest band to the land surface, and the air pressure of this
band indicates 1000 hPa in the image. What does '1000hPa' exactly
mean? Is that the height where the air pressure is exactly 1000 hPa?
Or... Is the value of 1000hPa just representing a layer ( i.e.
975~1025 hPa -> 1000 hPa; 925~975 -> 950 hPa... )?
If I missed something in my explanation and you guys don't understand
my situation, please reply me. Thank you in advance!
Harry from Korea
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| Re: Question on collection change - MOD07 air profile [message #55378 is a reply to message #55157] |
Thu, 16 August 2007 14:19  |
James Kuyper
Messages: 425
Registered: March 2000
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Senior Member |
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I passed your question on to our resident expert on MODIS Atmosphere
code, and he finally got around to responding - here's his response:
============================================================ ==================
Hello Dirty Harry,
Item 1
------
All Collection 4 profiles (temperature, moisture, and geopotential
height) previously included meaningless below-surface values. Now,
in Collection 5, fill values are being used below the surface
pressure. This impacts the level 2 profile products as well as some
level 3 temperature surfaces (1000 hPa, 850 hPa, and possibly 700 hPa
in areas of very high elevation). Since the total precipitable water
is integrated only to the surface pressure, this product is not
impacted.
Item 2
------
MOD07_L2 provides 20 pressure levels with pressure level 1 being the
highest above sea level (5 mbars). 1000 hPa (hectoPascals) are equal
to 1000 millibars of air pressure.
Data referenced to a particular pressure level should, where possible,
be interpreted as applying on the surface at the corresponding
pressure, not as an average or total over a range of pressure levels.
> From: DirtyHarry
> Date: Fri, 03 Aug 2007 06:29:31 -0000
> Subject: Question on collection change - MOD07 air profile
> To:
>
> Goodday, Everyone...
>
>
> Our research team is currently studying on several meteorological and
> ecological topics with various MODIS products. At this point, we are
> trying to compare MOD07-retrieved air temperatures with those measured
> from 72 locations of national weather stations in Korea.
>
> To do this, we have used MOD07 collection 4, but recently we found
> MOD07 collection 5 have been already provided. Now I have two
> questions.
>
> 1. We checked the images shown in MODIS official website and compared
> collection 4 image with collection 5 image at the same day. We found
> air temperature at near-surface level (i.e. 20th band) mostly appeared
> on the land part of the collection 4 image. However, Air temperature
> at near-surface level was black out in the collection 5 image. We are
> very curious about this phenomenon. Why is it?
>
> 2. MOD07 provides 20 bands. If I understand correctly, 20th band is
> the nearest band to the land surface, and the air pressure of this
> band indicates 1000 hPa in the image. What does '1000hPa' exactly
> mean? Is that the height where the air pressure is exactly 1000 hPa?
> Or... Is the value of 1000hPa just representing a layer ( i.e.
> 975~1025 hPa -> 1000 hPa; 925~975 -> 950 hPa... )?
>
> If I missed something in my explanation and you guys don't understand
> my situation, please reply me. Thank you in advance!
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