The Digicora MW11 receiver/processor unit deciphers RF communications transmitted from a compatible radiosonde (RS-80 series) through a tunable receiver and 400 MHz antenna. Receiver positioning for launches requires a local LORAN-C receiver/antenna sub-system, even if the receiver is stationary. The Digicora can be operated in one of two modes: Standard or Research Mode. With Standard Mode, the Digicora collects and performs real-time quality control of radiosonde data until it detects a pressure increase (due to a balloon burst). After the flight, the Digicora can be queried for coded messages. In Research Mode, the Digicora collects radiosonde data on descent as well as during ascent. There is no real-time data quality control with Research Mode, however, so there may be dropouts at sporadic intervals. Also, this mode does not offer coded message output.
The Digicora unit is quite heavy (> 140 pounds) and must sit upright as access to the front panel is required. The upper surface of the Digicora is robust, so equipment, such as a laptop for data collection, can be placed on top of the unit.
Cabling is required to two antennae: a local LORAN-C antenna and the UHF antenna. Both of these antennae need to be mounted outside with as clear a view as possible.
A PC/laptop can be used to receive output from the Digicora through one of its COM ports and just about any communication software package. An older laptop is included with this setup (Dell 133 MHz with Windows 95). This already has Procomm Plus for Windows installed and a script setup to do the data collection. Software to plot data from a radiosonde flight is also included.
Although steps have been taken to try to make the data collection process mostly "self-documenting," it is strongly advised to have (and use!) a logbook to annotate details about each launch. Six weeks following the experiment, when you've finally found time to work on the data, it is always surprising to find out how little you can remember about a particular launch.
Initial Equipment Setup and Interconnects.
Local LORAN-C Antenna. Mount the local LORAN-C (whip) antenna somewhere with a good exposure to the sky. When attaching the base of the antenna to a vertical post, take care not to compress the interconnect cable attached to the outside of the lower portion of the antenna. The LORAN-C whip antenna screws into the top of the base section. Connect the local LORAN-C antenna to the Digicora unit with the included cable (100 ft, RG-58). The Type-N connector screws to the pre-amplifier unit on the antenna base, and on the Digicora, the connection is a BNC connector labelled "LOCAL LORAN." There is also a pen marking this location (there are three other BNC connectors in this area). Keep loose cables out of traffic to avoid stressing this connection.
UHF Antenna. The UHF antenna has a base designed to accept a standard pipe size (2"). I've included a section of plastic tubing. If the mounting does not require the extension, you can use hose clamps to attach the upper section only. This antenna should be positioned with good sky exposure, as the RF from the radiosonde is line-of-sight. If there are nearby antennae, especially operating around 400 MHz, there may be interference. The 100 ft cable has Type-N connectors on both ends. Screw one connector onto the grey pre-amplifier box on the antenna and the other end on the side of the Digicora (see a pen label indicating "403" where you need to attach).
Digicora to PC Connection. On the side of the Digicora, you will find six DB-25 ports. The back-most port (P1) needs to be connected to the PC with a DB-25 to DB-9 cable (included with the laptop). Connect the DB-25 end to P1 on the Digicora and the DB-9 end to COM 1 on the PC. The communication interface is set to 9600,8,1,n, with the PC receiving ASCII data from the Digicora. The Digicora is set to operate in the Greenwich time zone (GMT/UTC), so it is highly recommended that the PC/laptop time reference also use this time zone. This will help to alleviate problems with file naming conventions done with the data collection software. We are, after all, meteorologists and our time zone is GMT!
The power cord for the Digicora unit attaches to the connector on the bottom of the side panel. Requirements are standard 120 VAC/60 Hz. A switch (labelled "Mains") on the upper section on the connector side activates the power--be sure to turn this on. The switch is lighted (and flickers a bit).
Steps to Performing a Radiosonde Launch with Digicora System.
There are a number of steps to doing a radiosonde launch: (1) setting up the Digicora and PC data collection, (2) preparing the radiosonde, (3) inflating the balloon and attaching the parachute and radiosonde, (4) obtaining surface observations, (5) securing permission from local airports to launch, and (6) doing the launch and making sure data are being collected.
The following description covers all the various facets of performing a launch with the Digicora. Some of the sequencing can be changed (e.g., surface observations can be entered before the launch), so feel free to experiment with the order. Some precautionary details are included that are critical to achieving a successful launch, along with some notes.
Note: If this message comes up every time the Digicora is powered up, refer to the SSTR adjustment sheets. You may want to adjust the electronics to impedance match the UHF antenna/cable. You will need a voltmeter with small clips and a small screwdriver.
The Digicora will now display the current date and time (GMT). Push the C4 button to ACCEPT the time, unless the clock is off significantly. In this case, press the C5 (Reject) button and enter the correct date and time using the numeric pad. You will be prompted for a 2-digit year (press "0" then "6" on the numeric pad for 2006, then press "ENTER"), 2-digit month, 2-digit day of month, 2-digit hour (GMT) and 2-digit minute. Once completed, you'll be returned to the original date/time display to "ACCEPT" the current values (press C4 to Accept and continue).
"Select Operation" will be the next option displayed on the Digicora. Choose "SOND" by pressing the C1 button. This will load the program from ROM. Note this takes up to five minutes! The top line of the display will show " * Loading SOND " and "SOND" will be flashing on the second line of the display as the program is being loaded.
After SOND has loaded "Select sounding mode:" will be displayed on the Digicora screen. There are two choices here: "Research" or "Go_on." If you are planning on sampling during descent, doing an "up/down" launch, select "Research" by pressing the C4 button. This bring up a display "Research mode for :" and prompt you to choose PTU, Wind or Both. Our experience is that this option really doesn't matter, and Both is preferred. Choose "Both" by pressing the C3 button. On the next screen, you'll see the word "Research" displayed at the right on the top line. Press the C5 button (Go_on) to continue. If you are doing an "up only" launch, simply press C5 ("Go_on") at the first display.
The next display will ask "Which wind measuring method ?" with choices of OMEGA and LORAN-C. Choose LORAN-C (C2 button). After a few seconds of loading the wind software, you'll see the "Station Position: Latitude Longitude and Altitude" If the values are correct, press the C4 button (ACCEPT). If they need to be changed, press the C5 button (REJECT). If REJECTING, you will be prompted for entry of Latitude. Use the numeric pad to enter the new latitude (use dd.dd format) and press ENTER when done. Next, choose from NORTH (C4) or SOUTH (C5). Next, enter the new longitude (positive number only) and choose EAST (C4) or WEST (C5). Finally, enter the staton altitude (in meters). You will return to the original "Station Position..." ACCEPT/REJECT display. Press C4 (ACCEPT) to continue.
"Start Mode" is next with a choice of AUTO or MANUAL. It is recommended that you select AUTO unless you are using the sonde with a kite flight or doing testing without actually flying a radiosonde. In AUTO mode, the Digicora will detect the launch by tracking the pressure. When a decrease of about 30 hPa has been seen, you will be notified of the launch starting. Data from the start are saved in a buffer, so no low level values will be lost.
If you select MANUAL mode, the operator must press a button to start the data collection! For this reason, it is highly recommended that the AUTO method be used for all "normal" flights. Many MANUAL starts have resulted in missing data at low levels because the operator was caught up in all the excitement at launch...
After choosing the start mode, the display will show "Calibration coefficients: Put tape in or press C5 to use keyboard!"
At this time, the Digicora is at a position where it can be left for a while so the balloon can be inflated and the radiosonde prepared.
Do not run the tape through until the radiosonde has been activated! The reason for this is that the Digicora immediately attempts to start "listening" for the radiosonde. If the battery is not activated and attached, the unit will BLEEP at you incessantly until the radiosonde is active. If this happens, be calm and press the "CLEAR" button on the keypad to quiet the BLEEP BLEEP BLEEPing for a while.
(3) Prepare the radiosonde and inflate the balloon. Both of these tasks can be done before setting up the Digicora. Since the battery takes a while to charge up (water activated), it is a good use of time to do this, then inflate the balloon. By the time the balloon is inflated, the battery should be ready. Be sure to turn off the gas flow with the main cylinder valve when done – do not rely on the regulator shut-off valve!
Radiosonde preparation. Remove the radiosonde from its foil pouch. Find and remove the battery and cut off the top of the battery foil pouch. Pull out the battery and reinsert it with the lead wires coming out of the top. The pouch makes a convenient wetting container. Fill the pouch with plain water until it covers the whole battery by about 1/2". It takes about 3-5 minutes for the battery to become fully activated.
The RS80 Radiosonde User's Guide (included) covers details on the "official" method of preparing the radiosonde. There are nice close-up photos showing how to remove the sensor boom cover.
On the opposite side of the radiosonde, you should find the calibration paper tape. This is critical, so avoid tearing the strip. Each radiosonde is factory calibrated, so it is a good idea to not have a bunch of them lying around--get rid of them once the launch is completed.
The temperature/humidity sensors on the radiosonde are covered with a plastic housing. Carefully remove this housing (see RS80 User's Guide). Gently fold up the flexible sensor boom, so the sensors are exposed. Do not touch the temperature probe. The humidity sensor should have a moisture protection hood. If is has fallen off, it can be shoved back over the sensing portion.
When the battery is activated, drain off the excess water (note: this water is acid contaminated) and shake out excess water. Insert the battery into the radiosonde pocket and attach the leads (leads should be on the up side to prevent water from getting on the connection). Fold the cover back over the battery and secure with the interlocking flaps (perhaps also use the rubber band or some tape, if you are unsure about the flaps).
Note: The battery generates heat and this could damage the sonde if left for extended periods (> 30 mins) while the sonde is "on the ground." The battery will power the sonde for at least four hours, but try to minimize the length of time the battery is in the sonde while on the ground.
The transmitting antenna is the blue wire at the bottom. It should be straightened.
If possible, set the radiosonde somewhere stable (out of direct sunlight) and position it so that it is upright (allowing battery fluid to drain away). Unfurl the radiosonde LORAN-C antenna from the "wedge" (about 10 ft) and lay it out so it can start receiving LORAN-C position information. The antenna portion of the lead line has a red wire cured around the white wire. This gives the radiosonde LORAN-C receiver the best opportunity to detect chains. You may want to make up some sort of holder allows this antenna to remain extended during the pre-launch period.
Balloon Inflation: General.
Operational radiosonde launches try to achieve a set ascent rate (6-10 m/s). This is done for a couple of reasons: to complete the launch within a given time period (to 100 hPa in about 30-45 mins); and to adequately ventilate the temperature and humidity sensors. In practice, however, this can be difficult to accomplish, especially if you are doing the balloon inflation outdoors. I've included some "official" inflation weights to allow you to fill the balloon to a point where it will be neutrally buoyant with a given weight set. You can experiment with various weights and desired ascent rates. Note that during precipitation, any liquid water accumulated on the radiosonde train will eventually freeze and add mass to the load. Additional lift may be required to get the radiosonde above the freezing level during precipitation.
If you are inflation the balloon in an exposed area, the balloon may be difficult to handle in moderate to high winds. You may want to use a long string tied to a solid point on the ground to act as an anchor in case the balloon gets away from the holder.
Balloon Inflation: Parachute Launches.
If you are doing an "up/down" launch, you will need a parachute. Once the balloon has been inflated, tie off the neck of the balloon near the center with a short piece of string/twine.
Open the parachute package and jank on the strings to clear the knots. You should be able to make the parachute open easily before attaching it to the balloon. Slide the loop at the top of the parachute over the balloon neck, then fold the lower portion of the neck upward. With some string, firmly tie the neck just above the loop of the parachute. The neck ends up supporting the parachute, and the radiosonde is attached to the bottom of the parachute.
The RS80 User's Guide recommends using some sort of cardboard when using a parachute. This is to minimize twisting while the radiosonde line is derailed. Our experience shows this is not necessary. It increases complexity and litter, and adds mass to the radiosonde train.
Balloon Inflation: Non-parachute Launches.
If you're doing an "up only" launch, you may choose to not use a parchute. Use some string to tie off the neck of the balloon near the middle. This is done to allow attachment of the sonde by folding the neck once again, tying it up and inserting the "claw" of the "wedge" into this fold. An extra knot or two after folding the neck over will help secure the wedge to the balloon neck.
After entering the calibration coefficients, you are likely to encounter a series of annoying BLEEPs along with a display of " * CHECK TELEMETRY." If telemetry is set correctly before running the calibration tape, this can be avoided and the display will show "Monitoring sonde" along with decoded data from the radiosonde.
Several critical events happen at this time, so pay close attention to the display.
Telemetry. If the Digicora is not receiving signals from the radiosonde, you will hear an annoying "BLEEP" from the Digicora, accompanied by a flashing display of "CHECK TELEMETRY!" To stop the "BLEEPs," push the "CLEAR" button on the right side of the keypad.
The Digicora is set up to start with a default frequency of around 403 MHz, and the factory default setting for the radiosondes is (fortunately) pretty close to this value.
To adjust the Digicora receiving frequency, press the "TELEM." button on the front panel (bottom left). This will bring up the tuning display. Turn up the volume by pressing one of the ")))" keys on the far right of the front panel--there are four possible levels. Hearing the radiosonde "music" helps to adjust the frequency. If you don't hear anything but static, press the "SCAN" button. You'll see the frequency scroll and stop when the Digicora recognizes the radiosonde. This frequency should be somewhat close to 403 MHz. If not, say it is around 405 MHz, you may have locked onto a side-lobe. Manually "Tune Up" or "Tune Down" until you hear a clear "tune" and the frequency is near 403 MHz. The number of stars "****" should be at least four on the right side of the display.
When the frequency is where it should be, verify that the display shows "Afc" to the right of the frequency. If it shows "Trck" there is a danger the receiver will drift onto some other stronger transmission. Track is used if you are tuning the radiosonde to another frequency. Refer to the RS80 User's Guide on how to adjust the sonde transmission frequency.
Press the "TELEM." button again to exit the tuning section and return to the "Monitoring sonde" display.
Note: It is advisable to pre-tune the Digicora before running the calibration tape through. Once the battery is attached, follow the steps above. This will avoid some of the confusion. After the telemetry is set, return to the "Calibration…" display by pressing the "TELEM." button again.
Loran-C Synchronized. At the same time that the telemetry may require your attention, another important event will hopefully occur. This is the "LORAN_C Synchronized" message, which is accompanied by the annoying "BLEEPs." This important message indicates that the receiver's LORAN-C has successfully started decoding LORAN-C transmissions and is working properly. Hit the "Clear" button to stop the "BLEEPs."
If you encounter a display "Loran-c not yet synchronized" with options to "WAIT" or "GO ON" choose the "WAIT" option. Also, check your cabling to the antenna. Typically, LORAN-C will synchronize within a minute or two, but in some conditions it may take up to 10 mins to lock in.
After successfully negotiating the telemetry and LORAN-C events, the "Monitoring sonde" window should now show radiosonde data as they are received. On the upper line, you should see the number of seconds elapsed, pressure, temperature and humidity. These "RAW_PTU" values should be eyed carefully to evaluate their validity. If the radiosonde is well exposed and out of the sun, the values should be very representative. If you have independent PTU (Pressure, Temperature, Humidity) data, note any glaring differences that would not be attributable to the sonde position. If the values are way off (e.g., pressure reads 840 hPa at sea level), then the sonde should not be launched. The humidity may read strange if the sensor has been damaged (missing values are reported as "/////"). Experience with these Vaisala sondes has shown that they are 90+% reliable. If a sonde is bad, save it (along with the calibration tape) so it can be used as a "show-and-tell" item for other classes. You may want to dismantle the radiosonde to see the inner workings. These model radiosondes are no longer manufactured.
Note: If you encounter a bad sonde, you can use the battery from this radiosonde on the next one. This will save time during the scramble of swapping over to the next sonde. Keep track of the calibration tapes!
RELEASE. Within a minute or two, your should hear another "BLEEP" and see the word "RELEASE" flashing on the left side of the display. This is a good indication, meaning that all the right things have been detected by the receiver/processor. If you have not encountered the "RELEASE" message, do not launch! It would be better to be patient and wait a bit longer. The Loran-C synchronization can take quite a while. If things are not working right, you can hit the "Reset" button and go through the Digicora setup again.
Surface Observation. While in the "Monitoring sonde" display, note the PTU values, as they may be needed for input as the surface observation. Soon after the sonde is launched, the Digicora will prompt you for these values, as well as the surface wind speed and direction. Since the Digicora uses the surface observation as a baseline to compute geopotential height, the radiosonde pressure value should be used (even if different from independent measurements by as much as 5 hPa). If you have independent trustworthy temperature and relative humidity data, these should be used, as the sonde is likely to be in a less optimal location for sampling these data.
If the launch requires a parachute, attach the sonde to the base of the parachute using the "claw" of the plastic wedge. Insert the "claw" through the slot of the parachute and insert the extra material in the "teeth of the claw" to give additional holding power. If you are using a string parachute attachment, tie the "claw" securely to the strings at the base of the parachute.
If the launch is without a parachute, fold the neck of the balloon over so there is a "slot" where the claw of the plastic wedge can be inserted. Tie off the fold securely and slip in the "claw"-- the teeth will prevent the wedge from dislodging from its attachment to the neck of the balloon.
(5) Just before launch. If there are people available to assist, have someone hold the neck of the balloon and parachute, while someone is holding the sonde with the radiosonde's LORAN-C antenna extended. Try to keep the radiosonde LORAN-C antenna extended/well exposed so it can receive LORAN-C data during the pre-launch handling. If doing the launch "solo" then it would be wise to check the Digicora just prior to launch, with the radiosonde positioned so it can receive LORAN-C data with its antenna extended.
Monitor the sonde LORAN-C reception. Press the "STATUS" button, then select "LORAN". This will display LORAN-C stations received by the sonde (two chains sets are displayed). There should be at least three stations received by the radiosonde before launch to compute winds. The display will show signal strength of a chain's station when it is received (0 = weak, 9= strong).
If there are less than three LORAN-C chains consistently reported on the LORAN status display, the flight will not compute winds at low levels!
Have the person holding the sonde change position (orienting the Loran-C antenna differently) if there are less than three LORAN-C stations in view. Wait for about a minute to evaluate the sonde reception of LORAN-C chains. Once the display of chains has become stable (3 for more reporting), the launch can proceed.
If there are any local clearance requirements needed to do the launch, take the necessary steps. A nearby airport control tower (and pilots) would probably like to know that you are about to launch. The tower people can let you know of any incoming or outbound aircraft that may be impacted.
Verify that the PC is indeed capturing output from the Digicora to a file by seeing the capture net depressed!
Once satisfied that all is in order (things can get a bit chaotic at launch time!), it is time to let it go!
Gauge your release point so that the ascending "train" will not encounter any overhanging items. If launching near a building, be aware there may be eddies on the downwind side. The tether line is 200 ft long and it will be let out at about 5 m/s.
Let go of the balloon and radiosonde at the same time, once you are ready. The balloon should lift off and the radiosonde line should start unraveling from the plastic wedge. If the balloon is under-inflated, there is a chance that the sonde may drop faster than the balloon ascent rate.
A radiosonde launch is usually an exciting event, attracting lots of attention. Try to not get caught up in the excitement.
Next, you will be prompted to enter the surface observations. Key in the values (pressure, temperature, then relative humidity). You will be prompted to ACCEPT or REJECT your entries. Next, you will be prompted for wind speed and direction (note: the wind speed units are m/s). Key in these values and ACCEPT.
If you have used the MANUAL start mode (and pressed "START"), you will be prompted for surface observations at this time.
Note: You can enter the surface observations before the launch. This is done by pressing the C# key below "SFC OBS" on the "Monitoring sonde" display. My personal preference it to do it after the launch to insure that the most recent data (matching launch time) are used, if independent measurements are available. Also, the given radiosonde may be faulty and extra time is required to prepare a replacement.
About two to four minutes following the start, data should start scrolling to the PC at 2-sec intervals. Verify that the capture is indeed turned on!
During the flight, you can monitor the sonde output on the Digicora data display. Press the "DATA" button and choose a display option. RAW_PTU will show elapsed time (since launch start), pressure, temperature and relative humidity. Press the "HELP" button and the top line will become a header line. These data are updated at 1-2 sec intervals. EDT will show data passed to the PC (channels up to dewpoint). STD will display mandatory levels as they are encountered (sonde must pass through each level before that level is displayed). WIND will show the wind data (also sent to PC). Winds are only updated at 10-sec intervals.
You will probably encounter the annoying "BLEEPs" during a flight, so it is best to hang around after the flight starts. Usually, this is a "CHECK TELEMETRY!" message. The radiosonde frequency may drift with time and this drift may be faster than the Afc can follow. Hit the "CLEAR" button, press the "TELEM." button and try "Tune Up" or "Tune Dn" to get better reception. Be sure the display shows "Afc" before exiting the telemetry display.
If you see dropouts in the PTU channels or computed winds, this is due to either bad reception or, for winds, the number of sonde-detected LORAN-C chains dropping below the minimum required. Other than improving the tuning, there's not much that can be done (except hope for the best!).
On the PC data display, the channel to the right of elapsed time is the ascent rate. Note that these data lag the real-time data by a few minutes! Data scrolling to the PC are fascinating to watch, especially when there are atmospheric features (strong inversions, low-level jets, etc.).
Since post-flight data are available, it would be wise to collect them. You can append the current capture file (may cause plotting problems?), or close the flight capture file and open a new one to capture the messages. Typically, an "Up Only" flight will take the better part of an hour, so you can use the same script to open a capture file for the messages (likely to be an hour difference in the filename). Alternatively, you can write your own script to collect the messages using a different naming convention.
Messages are sent to the PC by simply pressing the corresponding C# button. Wait for the message to finish before going on to the next message. Available messages are: TEMP -- coded rawinsonde message, PILOT -- winds at Pibal levels, LIST -- plain language version of TEMP listing, and STATUS -- a listing of codes relating to data quality.
Ending the flight -- "research" mode. Data flow to the PC will stop with the sonde hitting the ground and either surviving or being destroyed (accompanied by loss of signal). You may also loose telemetry if the sonde has blown over the horizon. If you want to manually end the flight, get to the "Monitoring Sonde" screen, then press the CMND button. This will bring up a screen showing RAW_PTU data and a "STOP" button. To end the flight, press the C1 button below the "STOP." You will be asked if you want to end the flight, choose the C# button below the "YES" label.
Some additional data, at levels lower than shown on the PC, may still reside on the Digicora. If these data are critical, get to the "RAW_PTU" display and use the Up arrow (left of the keypad) to scroll back within the data buffer. Values can be hand written from the display, or typed in on the PC. Note that only the PTU data reside in this buffer. Winds are not available below the lowest level (on descent) reported on the PC screen.
Once all possible data has been extracted from the Digicora, you can safely power it off by pressing the "off" button. You can safely leave the unit powered up if the next launch is imminent, and simply hit the "reset" button when the time comes.
Ending PC File collection. The data sent to the laptop need to be secured by clicking on the "fishing net" button. This will close the capture file. Be sure you have noted the capture filename in the log book.