The ARM NSA Barrow site has two operational Vaisala radiosonde systems, both based on the DigiCORA III product version. One is a manual system, located in the Great White shelter, the other an Autosonde (automatic balloon launcher) located in its own shelter and platform. In OSS, these are represented as two separate systems, BBSS and BBSS(Autosonde), respectively. As of the second half of 2011, twice-daily operational radiosonde launches have been switched over to the automatic system. As of mid-2012, the Autosonde functions well with only minor hiccups.
In addition, a functional DigiCORA II system, which as of now (July 2012) has reached the end of the product lifecycle and can't be upgraded any longer, is kept as a spare. Its components are listed in OSS in the "NSA C1 Spares" location with a status of OUT-SPARE.
If not specifically indicated, all the following information refers to the Autosonde (automatic balloon launcher) and its components.
ARM's service contract with Vaisala covers a yearly maintenance visit of a Vaisala engineer. The full maintenance and testing process takes approx. 2.5 days to complete.
Description of the DigiCORA III Autosonde in normal operation
Three computing units are part of the DigiCORA III Autosonde system:
- The "local desktop computer" located in the Autosonde shelter
- The "remote desktop computer" located in the ARM Duplex office
- The "sounding processor" (Vaisala SPS311) also located in the Autosonde shelter
The local desktop computer runs Windows Server 2003. It is connected via the instrument network directly to the sounding and loading electronics and runs the software application that allows to control them. The main menu items and functions are:
- Loading of launch-ready balloons (with sondes attached)
- Tray operations and status verification
- Service mode for the installations and its various aspects
- Schedule launches, either recurring or one-off (for example, for IOPs)
Sounding data (D:\SoundingArchive) and logs are also stored on the local computer and can be collected from it.
The remote desktop computer allows for completely remote operation and troubleshooting of the system provided there are sondes loaded in the launch trays and helium available for filling balloons. Error and warning messages are automatically transmitted from the local system to the remote system and appear as pop-up windows. The main application is the Remote Monitoring window, in which the locations managed by this remote unit are displayed. In the ARM NSA case, this is only one: NSABARROW. Double-clicking this location item will open the ("Doris") log viewer. The computer also allows complete remote control of the local system via a Remote Desktop Connection. The computer runs Windows 7 and is connected to the office network without internet access.
The Sounding Processing Subsystem (SPS) is a proprietary Vaisala component that processes sounding data. It also connects to the GPS antenna and provides the authoritative timestamps for the datastream. This is a Vaisala-branded box without dedicated keyboard or monitor. It runs a version of Windows but is not serviceable by the operations team and not intended to be accessed.
Last upgrade of Autosonde DigiCORA III system:
- 3.64.1 -- DigiCORA software (attaching to a sounding, managing settings and parameters)
- 3.64 -- Metgraph software (graphing the data)
- 3.64.1 -- Autosonde software (loading, scheduling, controling and servicing the automatic balloon launcher components)
Upgrade carried out 2012-07-16 during the annual maintenance visit. The manual DigiCORA III system was previously upgraded to the same version. As of mid-2012, both systems run identical software.
How to load balloons
The automatic tray wheel has a capacity of 24 balloons with radiosondes attached. The entire process is guided by the Autosonde software running on the Local Computer. The tray wheel advances and the door to the robot room opens and closes automatically at the appropriate moments. Sequential loading allows to fill up a partially emptied system most efficiently. There is also the option to load balloons one-by-one. While the process is not hard, a new operator will need training beyond this description.
The steps for sequential loading of balloons with sondes attached are:
- Unpack a new radiosonde and insert it into the Ground Check Set.
- Start reconditioning of the sonde via the GUI software. Reconditioning involves bringing up the sonde to a set temperature and then checking T, RH, P against references. The process takes 5 min per sonde.
- While the sonde is being reconditioned, insert a black plastic nozzle into a new latex balloon and place it on the next free tray that has advanced to the door.
- When reconditioning is finished, attach battery pack to sonde and test the battery via the test button
- Place sonde on tray, lift up sensor boom, remove plastic retainer from spool and hook the spool into the ballon's nozzle.
- At the last step of the process, enter your initials into the software comment window.
- Go back to 1 to recondition the next sonde.
Reconditioning of the next sonde can already happen while attaching the previous sonde to the balloon and carrying out the last checks. On the average, with sequential loading, loading new balloons takes approx. 8 min per sonde. (This varies with operator experience.)
How to start a sounding
If a one-off sounding is to be carried out ("let's launch a balloon now"), and the Autosonde system is operational and has at least one ready tray filled with a sonde + balloon, there are two ways to proceed. Both use the software installed on the Local Computer:
- Use the Schedule menu item to schedule a single one-off launch
- Use the New Sounding button at the top left of the window to initiate a sounding and manual launch. This button is identical to the one in the manual DigiCORA III system.
These steps can be carried out via remote desktop connection from the Remote Computer. Note that the RDC needs to be closed down immediately afterwards to avoid errors due to connection timeouts.
How to monitor a sounding
There are two ways of monitoring a sounding in progress:
- On the Local Computer, right click on the Active item below the New Sounding button and select Attach. This "attaches" the monitoring and graphing software to the sounding data that is currently being collected and allows real-time display of a number of types of data visualizations. From the Remote Computer, this can be achieved via the remote desktop connection, but if an entire sounding is monitored, care needs to be taken to avoid time-outs of the connection (for example by moving the mouse and changing the display every few minutes).
- On the Remote Computer, the Remote Monitoring window transmits messages sent by the sounding software. This includes warnings and errors but also notifications of the normal stages of a sounding.
Tips, tricks and pitfalls
There are three locations where configuration options can be set:
- via the Vaisala GUI software (DigiCORA and Autosonde)
- via a configuration file ("parameters" in the \bin directory)
- via the Windows registry
The DigiCORA system receives time settings via its GPS card. The GPS time signal is then corrected (leap seconds) by the SPS. This time is used for data timestamps, but is also intended to be used to set the computer time on the local desktop computer. Due to a defect (bug) in the DigiCORA or Autosonde software, which is not yet corrected in v. 3.64.1, this configuration can lead to errors or warnings, in particular during serial sonde loading. It was therefore disabled in 2011.
It is also possible that there are interferences between the GPS-provided synchronization and other methods to set computer time, such as via an NTP server (ntp-nsac1 on the local network) or the Domain Time II software that is part of ARM Core PC.
There are multiple configuration options in the DigiCORA software for time synchronization. These are set in the Windows registry on the local computer. Changes should never be made without advice from the Vaisala staff. In July 2012, the system was left to synchronize via Domain Time II, but only once a day during times where no sonde launch was scheduled.
The time synchronization bug will be corrected in the next software update.
Beware of remote connections
The remote computer can be used for complete remote control of the Autosonde system via an embedded remote desktop connection to the local computer. This uses standard Windows components. One major pitfall with this method is that the RDC can be shut down by the host computer, or otherwise drop or time out. If this happens while a sounding is in progress, impact on the sounding data has been observed, or the local computer could experience errors.
Therefore, the remote desktop connection should only be used for the minimum time required (for example, to schedule launches), and if possible not during a sounding. If it is needed to monitor a sounding (via the "Attach" menu item) it should not be left to idle and closed down once normal operation has been ascertained. Do not let the remote desktop connection time out: move the mouse or change tabs every few minutes. If sufficient, it is better to monitor only via the messages in the Remote Monitoring window and re-play the sounding after it is completed.
Computer reboots before launch
In order to clear any hung application or stop unnecessary services that may have been launched, the local computer will start each sounding preparation by executing a reboot. All required services and applications will launch automatically.
System refuses to launch
A reason why the system may not launch a sonde is that it could be in Service Mode. Several errors may then appear in the logs:
- system in Service Mode ==> no sondes will be launched
- system in Service Mode ==> compressor will not run ==> air pressure (to move trays) will drop ==> no sondes can be launched
Service Mode is enabled manually, which makes it unlikely, but not impossible, for the system to enter this mode accidentally
Flow and ascent rate
The ascent rate of the balloon is controlled by the flow rate of helium when filling the balloon. The latter is logged and set in the software. Good values (for NSA Barrow) are:
- Ascent rate: 5 m/s
- Helium flow rate: 250 l/min (Vaisala recommendation: 350-550 l/min, but lower values are ok, though balloon filling is slower).
A balloon filling uses approx 1100 l of helium gas.