NCAR Radiosonde Launching Procedures

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).

·        Import the sounding data into the Aspen software, on the WindCube laptop (or your own laptop). (See https://www.eol.ucar.edu/software/aspen for download.)

·        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.