NCAR Radiosonde Launching Procedures
Instructor: Tim Lim
Authors: Paul
Quelet & Joseph C. Y. Lee
Last Updated: 6-Mar-15
*** Start 20 to 30
minutes early to ensure you can launch radiosondes as close to the right local
time (8 am, 12 pm, 4 pm, 8 pm SHARP)
as possible. The radiosonde time is shown at the bottom right corner in a grey
box in UTC time. ***
Definitions & Facts
MGAUS = Mobile GPS
Advanced Upper Air Sounding System
NCAR uses the Vaisala radiosonde
system. It records at 1Hz temporal resolution.
Variables Measured through
Soundings
1)
Temperature (T)
2)
Air Pressure (p)
3)
Relative Humidity
(RH)
4)
Wind Speed
(WS)—through the GPS
5)
Wind Direction
(WDir)—through the GPS
Radiosondes are still often
used for ground truth! Remote sensing can still be erroneous.
Radiosondes cost around
$200.00 per device.
The radiosondes rise
approximately 5.0 m/s as a standard. (This depends upon the balloon inflation
size for buoyancy). See the instructions on the volume of balloon inflation.
We are launching 100 g
balloons at the BAO, which can rise up to 20 to 25 km above surface.
Radiosondes can land 70-100
mi. from the launch point! The radiosondes launched in the XPIA experiment are
not coming back. They do not have self-addressed stamped envelopes, but only
the Vaisala website saying that it is save.
Do not worry about the
swinging motion direction of the radiosonde as it hangs from the balloon this
motion in the GPS is taken away in post processing because the length of the
cord is known and the calculation can be done.
Devices & Hardware
·
The most
expensive and sensitive part of the radiosonde is the temperature sensor along
with humicap capacitor. These are the fine wires in the middle top.
·
The humicap is
hydrophilic cap that changes the capacitance. In fact, since there are two
humicaps, the way Vaisala designed the instrument, the measurement and
reporting of data changes every 60 seconds. This is reflected in the data
display. One is always being heated and dried out while the other one takes
data, especially important in supercooled liquid water environments in
condensation.
·
The radiosonde
needs to be sealed because there can be condensation onto the radiosondes.
·
The helix metal
portion of the radiosonde is the GPS antenna.
·
There are no
parachutes on these radiosondes. When the balloon breaks, the device falls
around 35 m/s in the thin upper atmosphere. The device falls ~ 9-12 m/s in the
dense lower atmosphere. (This is comparable to a heavy snowball.) So far, no
problems reported with human head strikes.
·
Labview is the
software that NCAR uses on the MGAUS truck, derived from their dropsonde
software.
·
Unlike in the
original demonstration, there should be a table out at the BAO to set things up
on.
** Radiosonde Launching Procedure **
Setting up radiosonde:
1) Be sure to
launch a radiosonde from flat ground level away from the truck, any buildings
or other persons.
2)
You should see a
LabView software running on the screen, click “Soundings / Start” (should be
first button on the left)
3) After starting the LabView software, enter the “Mission ID” following format
here (in UTC): ‘MGAUS.VC.00.YYYYMMDD.HHMMSS’ Example: MGAUS.VC.00.20150309.120003
4)
Click Save &
Continue; Now a file named as “MGAUS.VC.00.YYYYMMDD.HHMMSS” would be created
5)
Click “Start
Channel 1”: The radio channel that connects computer, GPS and the radiosonde
6)
Get the
radiosonde out of the back of the truck and take it out of the silver-color
package, being sure to not drop it!
7)
At this point, in
preparation of the radiosonde, follow the instructions printed on the LabView
screen…
8)
Put the
radiosonde onto the port stand. Insert
the umbilical cord port to the bottom of the radiosonde correctly so that “UP” is facing up.
9)
Recondition the
humidity sensor by putting the radiosonde on the GC25 ground receptacle. Use
the arrows to toggle to the recondition the humidity sensor setup. Press Select (Finnish for “Press Enter”) to
recondition. Give the radiosonde about 3 minutes to setup a timer countdown.
10) Take the battery out of the smaller inner packaging.
Note the water jackets to keep the batteries at nearly constant temperature.
11) Slide the
plastic pins receptacle (with 2 small holes) out of the battery pack *top*
so they can be connected first. The battery back cannot usually be snapped on
in one single motion.
12) Set the tune frequency on the GC25 ground device if
needed. Press select if yes, you do want to change the transmission frequency.
13) For radio transmission 403.00 MHz is the default frequency. This frequency is usually fine as long as there are no other
instruments transmitting at that frequency in the area. The last frequency digit MUST BE AN EVEN NUMBER if a change is made.
14) (If needed, change the frequency either by using the
mouse or the clicking to toggle the frequency to AN EVEN number frequency.)
15) Select “Not Display Timer”.
16) Select “Disconnect”.
17) Now the radiosonde is reconditioned. Carefully
disconnect the “UP” cord, take it off the GC25 ground receptacle.
18) Push the pins
on top of the battery pack into the top of the radiosonde until
they are tight.
19) Push the whole battery
pack onto the back of the radiosonde, starting from the top to the bottom, so that it snaps
tight. You should hear a click. Try to pull and separate the battery pack and
the radiosonde to check if they stick together tightly.
20) On the computer, click “Continue” and now you should
see a spectrum. Each time lock onto the peak transmission frequency for
communication with the radiosonde. If you chose 403.00 MHz (default) as
frequency, you should see a huge signal peak (strongest signal) at 403.00 MHz,
matching well with the radiosonde. Drag the mouse to the signal peak and click
to rescale y-axis if necessary.
21) Click Save & Continue to advance to the next
screen.
22) Once you have finished the prelaunch procedures, at
this point the radiosonde will start trying to take data. Up to that point, all
the radiosonde values will be overwritten and not recorded.
23) By clicking Continue, all the data would be written to
new file.
24) After the radiosonde starts up after transmission and
communication, the calibration coefficients take ~30 seconds to become
calibrated. At the BAO, Tim would provide a table with a fan blowing at the
radiosonde to minimize moisture impacts for calibration.
25) Select “Transfer Value”: By doing so, you are
setting the current radiosonde measurements as surface measurement on the
ground.
26) Click Continue. There is a 10-second time lag for data
recorded from radiosonde to be shown on the computer screen.
27) Make sure the flashing lights for the temperature
and number of satellites settles down. In order to do this, you will
need to hold the radiosonde away from other objects and away from the middle of
your body.
28) DO NOT START PREPARING BALLOON UNTIL
ALL THE FLASHING NUMBERS ARE GONE. Make sure the radiosonde is working probably
BEFORE you inflate the balloon (you need at least one hand to hold the balloon).
29) IMPORTANT: Slightly bend the
temperature and moisture senor (the metal that sticks out) and click it to the
side (between two little plastic hooks) on top of the radiosonde, so the
sensors would be tilted. This
is CRUCIAL because we want to take measurements off the aerodynamic path of the
balloon when the radiosonde swings, as the balloon itself can reflect, absorb
and release heat and affect the measurements.
Inflating balloon and launching:
30) Now it is balloon time. In the back of the truck, put
the nozzle up the neck of the balloon about 6 inches or so. Make sure to hold onto the balloon
with your hand so it does not fly away during inflating the balloon.
31) Tim recommends starting to tighten a zip tie around the balloon neck and
nozzle as you are filling it to make the final tightening easier.
32) To start the flow of helium in the balloon, open the
large valve (on the top of the cylindrical gas tank) with a hand turn. Each
helium tank should be able to fill up 6 balloons.
33) Do not unravel the radiosonde to hang down much before
launching. Keep the balloon at some distance away from the truck.
34) There would be
a count near the set up. When the count increases by 20, then stop. For example, when the count start at 339, stop at
359.
35) Loop the balloon bottom around the radiosonde hook and
pinch this off with another zip tie
so it is securely fastened. This is a
bit tricky as a single person and takes some dexterity and practice. Do not let
the radiosonde go yet!
36) Make sure
the radiosonde tether string is not caught on anything before launch.
37) Once again, check the data the radiosonde is taking to
make sure it closely matches that of the WXT-520 and that the flashing lights
have settled down.
38) If the above procedures are correctly completed, the
radiosonde is already taking data…
39) LET HER GO!!
J (like the song)
40) When you go to the sounding software, you can close
the front screen that has the temperature and satellites.
41) The data can be monitored in real-time with the
LabView interface that has the tabs. It is fairly self-explanatory if you play
around with it.
42) Monitor the data appropriately for 40-60 minutes or so…
43) Cutoff the
radiosonde data collection sometime past 200 hPa pressure.
44) After a sounding has finished, you hope to click “Good Sounding” but there are other
options if something went wrong.
45) Name the
sounding following this format: ‘MGAUS.VC.00.YYYYMMDD.HHMMSS.txt’ (In UTC.) Example:
MGAUS.VC.00.20150309.120003.txt
46) Write down your name on the name line. Note:
These soundings are archived in a large national database for many years.
47) Write any interesting significant weather type things
or abnormal things in the notes section. Add a note saying “intended for
boundary layer purpose” as well.
48) Click “Quit” in the lower right hand corner of the
software.
49) Throw any trash away in a bag in the front passenger
seat.
Data Storage & Communication
·
File browse to on
board Computer C:\GAUSdata folder
·
Find the name of
your folder as named in the “Mission ID” step.
·
Locate the
D############_P.1 file, which is
your sounding data that continues to be updated until the sounding is killed.
The 999 values in the file are essentially NaN’s.
·
This is a
columnar text file that shows the measurements from the radiosonde.
·
Keep multiple copies of the data!
·
Copy the data to
the large (orange) external hard drive (should be at the BAO).
·
Write a summary of the sounding operations noting any
interesting features (e.g. low/high inversion, Low Level Jet, etc.).
·
Prepare the .png sounding from the Aspen software, and
the .png of the windspeed and wind direction.
·
Post the summary and images to http://a2expia.blogspot.com/ . (Note:
May need to have a personal flash drive or similar available as internet access
at the BAO will be limited, and the WindCube laptop should stay at the BAO.)
·
Additionally, copy the raw sounding data file to
breeze at /data/fielddata/XPIA/MGAUS.
Important Notes for XPIA
·
The new
radiosondes are in a box in the back of the MGAUS NCAR truck at the BAO. They
should stay in the truck so they do not take very long to be acclimatized.
·
Erie airport is
an uncontrolled airport so that there is no need to communicate when a sounding
is being launched. Since there is no tower control, only make sure an airplane
is not directly above you when you are about to launch!
·
Note that the
communication radio frequency is between 400-406 MHz. This is the part of the
EM spectrum set aside by the NTIA for meteorological transmissions.
·
The 400-406 MHz
frequency band should only ever be crowded if there are many meteorological
devices in the area.
·
There will be a
Vaisala WXT-520 short ~2m tower setup on a tripod at the BAO. This is an all in
one weather sensor. This will give the “ground truth” to compare against the
radiosonde when it is first turned on near the ground at the BAO.
·
Even though the
WXT-520 has an audio distrometer, it is not being recorded. There is
precipitation recorded at the LiDAR supersite for XPIA.
·
The XPIA project
is using 10 gram balloons these are the smallest balloons NCAR uses for
radiosondes, so that they have a very slow ascent rate for good vertical
resolution in the Atmospheric Boundary Layer.
·
The radiosonde
will hang a significant distance below the balloon so that the balloon solar
reflectance does not affect the true ambient conditions of the radiosonde.
·
Make sure to launch the balloon as close to the top of
the target hour, or a few seconds afterward, as possible. Use the UTC clock on
the computer display to verify.
·
Make sure the radiosonde goes up to at least 200 hPa.
It is somewhat uncertain where it will pop and start decent, but you have to
kill the data collection at some point.
·
Call Tim Lim if there is a significant problem you
cannot troubleshoot. 303-818-9906.
