Steps In MTP Post-Campaign Data Analysis
MJ Mahoney
Last Revision: July 15, 2008
5. Find radiosondes launched near the aircraft flight track
Radiosondes launched near the aircraft flight track are used for
several
purposes:
Great care must be taken in selecting radiosondes for the first two
objectives; different considerations apply for the third.
Before describing the how to find radiosondes launched near the
aircraft's flight track, I will briefly describe a change in file
structure that occurred during data processing of the TC4 campaign MTP
data in the fall of 2007. Prior to this campaign all RAOB data was kept
in a folder such as C:\MTP\RAOB\Missions\PAVE\
and in addition all the RSL-files were kept in the folder C:\MTP\RAOB\RSL\.This had the
advantage that the raodiosonde database was all in one folder, and all
the RSL-files were in one place. The disadvantage of this approach
however is that all of the relevant data for a campaign is not in one
place -- the mission data analysis folder (such as C:\MTP\Data\DC8\PAVE\). What I
realized when training another scientist to use the MTP software was
that it was tedious to move back and forth between the mission \Data\ and \RAOB\ folders. This was mainly an
issue when downloading RAOBs and when calculating retrieval
coefficients. As stated earlier, the main motivation for this
separation of RAOBs and data was to have a RAOB data base in one place.
Now that thousands of ROABs can be downloaded very quickly with the RAOBget program, the archival data
base is less important. It's simply easier and faster to download what
you need for a campaign than to dig through an archival database. So
the change was made: everything relevant to a particular field campaign
is located in the MISSION folder for that campaign (for example, C:\MTP\Data\DC8\PAVE\), and all the
RAOB information is now located in the \RAOB\
folder under this folder.
To determine which soundings to use as template profiles, copy the MISSION.RSL (or MISSION_All.RSL, wherever you stored
all the RAOB sites for the field campaign) file in the mission RAOB
folder (e.g., C:\MTP\Data\DC8\PAVE\RAOB\PAVE.RSL
described in Step 2.) to a file in the
mission data folder named MISSION_RAOBrangeAll.RSL
(e.g., C:\MTP\Data\DC8\PAVE\RAOB\PAVE_RAOBrangeAll.RSL),
which contains
a list of all the ICAO- or WMO-named radiosonde sites that the aircraft
might
have flown close to during the test, transit, and science flights. For
example:
ALB
APX
BGAM
BGBW
BGDH
BGEM
BGSC
BGTL
BMX
BNA
BOI
etc.
Figure 3. MTPbin Tools form.
Next, go to MTP Tools form (Figure 3) and select the Run Pgm tab. On the Flight Dates to Process frame,
select the Default All button
to select all flights in the default mission NUM file
in
the mission
folder (e.g. \PAVE\Setup\PAVE_NUM.txt).
If you don't want to use all the flights, select each flight
you want to remove and do so with the Remove
button in the Flight Dates to Process
frame. Then use the Save
button to save this list for future use; it will be saved in the
mission setup folder in a file named \MISSION\Setup\MISSION_NUM_batch.txt.
It can be retrieved in the future by depressing the Default button instead of the Default All button.
Finally, in the RAOB Range
frame, enter the maximum distance RAOBs in the MISSION_RAOBrangeAll.RSL file can be
from the
aircraft's ground track; the default is
160 km (~100 miles), which is about as far as you want to go without
there being overriding considerations. Also, enter the Minimum Pressure Altitude; the
default is 5.0 km. Since many RAOB launch sites are
located at airports, this avoids getting a lot of close approaches as
an
aircraft negotiates the ramps before flight and the skies after
takeoff. Also, low altitudes are not as useful for OATnavCOR
calibration because the high lapse rate makes small altitude excursions
affect the data quality. Finally, depress the Get RAOBs Within button. All
fligths in the Flight Dates to
Process frame will be processed and the results recorded in the MISSION_RAOBrangeAll.txt file in the
mission /RAOB/ folder. This
file has many uses during calibration and
retrievals, and has the following content:
Number
Year
Month Day UT0
LR11 LR12 Zb1 LR21 LR22 Zb2 RAOBs RAOBs
Ra1 Ra2 Zp(km)
1
2005
01 31 65.87 0
0 0 0
0 0 YRB
YRB 002.2 002.2 011.6
2 2005 01 31
67.51 0
0 0 0
0 0 YRB
YRB 064.4 064.4 011.3
3 2005 01 31
72.76 0
0 0 0
0 0 YZS
YZS 042.9 042.9 011.3
4 2005 01 31 78.25
0
0 0 0
0 0 YAH
YAH 020.5 020.5 012.5
5 2005 02 03
53.42 0
0 0 0
0 0 CHH
CHH 083.6 083.6 007.5
6 2005 02 03
54.46 0
0 0 0
0 0 OKX
OKX 041.9 041.9 010.4
7 2005 02 03
56.24 0
0 0 0
0 0 WAL
WAL 003.8 003.8 010.4
etc.
The first five columns contain a unique index number, the year, month,
and day of the flight,
and the UT of closest approach to the radiosonde launch site, for all
the flights in a campaign. The next 6 columns are blank, but will be
filled in later. The two "RAOBs" columns indicate the
ICAO name (or WMO name, if there is no ICAO name) of the RAOB site.
Initially, they will be the same, but if
spatial interpolation between sites is used when window corrections
and outside air temperature (OAT) corrections are calculated, they will
be different. (This is done later in a spreadsheet.) The next two
columns are the distance in kilometers of closest approach to each
radiosonde
site (the same initially), and the final column is the pressure
altitude (Zp) measured in kilometers at the time of closest approach.
The Minimum Pressure Altitude
captures most of the redundant sounding sites that would introduce
biases when we perform
the OATnavCOR. However, redundant soundings also occur because a change
in the
aircraft's heading near a sonde launch site can produce other points of
closest approach to that site. The MISSION_RAOBrange.txt
file in the
mission folder should be editted to remove any additional redundant
soundings (as objectively as possible!).
The blank columns LR11, LR12, Zb1 and LR21, LR22, Zb2 will be filled in
in a spreadsheet (see the next step) before
radiosondes are selected and retrieval
coefficients (RCs) are calculated. Each triplet of numbers indicates
how radiosondes that burst at low altitudes should be extrapolated to
higher altitudes.
The pair of triplets are the same if no spatial interpolation is to be
done.
Each triplet provides the lapse rate extension (LR11 and LR21) from the
burst altitude to a temperature break point (Zb1 and Zb2), and then the
lapse rate above the break point to 50 km (LR12 and LR22).
Figure 3. An example of how a
sounding that burst at low latitude is extended to higher altitudes.
This is made
a little clearer below in Figure 3, which
provides an example of
a sounding from Miramar Naval Air Station in San Diego (NKX) being
extended to higher altitudes. The left panel shows that the
NKX2005010200 sounding burst at 23 km (yellow trace). The Miramar
sounding 12 hours earlier (NKX2005010112) managed to get to 31 km
(light blue trace).
Since the two soundings are only 12 hours
apart, and are very similar before the former sonde burst, it is safe
to
bet that the early bursting sonde is similar to the other at higher
altitudes (above the burst altitude of 23 km). Sondes are extended by
using the triplet of numbers
described above: LR11=0.0 K/km - the lapse rate from the burst altitude
(23 km) to a laspe rate break
altitude (Zb1=25 km)
(where the lapse rate changes), and LR12=2.0 K/km -- the lapse rate
from the break
altitude (Zb1) to 50 km.
Figure 4. The RAOBman Filters tab.
The radiosonde database for a field campaign might include tens of
thousands of soundings for the purpose of selecting sondes to calculate
retrieval coefficients. It is convenient for some steps, such as
selecting template sondes, to create another RAOB file that contains
only sondes that were launched during the campaign. To do this, use
RAOBman to open the binary RAOB file containing all the soundings
(e.g., PAVE_All.RAOB2). Then
on the Filters tab, select
the time interval for the campaign. A few
days before and after the
campaign start and end dates should be included as well. (The reason
for
this is that occasionally a sounding may be missing for a particlar
flight, or it may burst at too low an altitude to be useful. In this
situation we may want to use an earlier or later sonde in its stead.)
However, some important quality control steps have to be taken before
doing this. This is expecially important when using the soundings to
calibrate the OAT or to calculate a window correction table (WCT). The
first test flight for the PAVE campaign was on Jan. 14, 2005, and the
transit flight home was on Feb. 09, 2005. Therefore, in the example in Figure 4, we selected the time
interval Jan. 12 through Feb. 11, 2005, for filtering files. We also
choose a minimum burst altitude of 20 km in the Valid RAOB Data Needed frame.
Figure 5. The RAOBman I/O tab.
Next, we need to specify on the RAOBman
I/O tab that we want the
selected files to be put in a new binary RAOB file. This is done in the
Random RAOB Output frame by
typing the filename (e.g., PAVE_Campaign.RAOB2)
in the Output File text box,
and then selecting the New File
option.
Figure 6. The RAOBman Select tab.
Finally, the Select button on
the RAOBman Select tab is depressed. To make
working with the Select list
box easier later, we next click the Sort
button to arrange the selected RAOBs into chronological order. Finally,
click the Write button to
write the selected RAOBs to the binary RAOB file PAVE_Campaign.RAOB2 that was
specified earlier on the I/O
tab.
Previous Step | Next Step
| Index |
