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MeteoSchweiz and the German Weather Service (DWD) lead an international project with the goal to intercompare atmopheric profiling systems. For this purpose, the two partners organize a measurement campaing in Linenberg, Germany, to perform simultaneous measurements with balloon sounding and remote sensing systems.
Upper air intercomparison campaigns are organized on the mandate of the World Meteorological Organization (WMO) for the purpose of getting an overview of the performance of the various operational upper air systems that are currently available . Such campaigns provide important information to national meteorological services (NMHS), who partially base the selection of an operational upper air system for their network on the outcome of these campaigns. Furthermore, these campaigns improve the quality and cost-effectiveness of upper air observing systems by providing recommendations on system performances, improvements of instruments and methods of observation and suitable working references, to WMO Members and instrument manufacturers. The focus of the Upper Air Instrument Intercomparison 2021 (UAII2021) is on radiosonde systems and aims to include as many manufacturers as possible. One of the additional aims of this campaign is to involve a variety of other measurement techniques such as remote sensing, aircraft and satellite observations to assess the added value of these instrument systems for upper-air observations.
Goal of the campaign
The main objective of the upper-air intercomparison campaign is to test the performance of operational radiosonde systems and to provide guidance on their performance relative to each other, as well as to evaluate the current capabilities of surface-based and space-based remote sensing instruments, and aircraft-based observations. Its results shall help WMO Members in selecting observing systems according to their requirements and will allow them to evaluate the potential offered by remote sensing instruments to complement the in situ information provided by the radiosondes.
The primary goals of the campaign are:
1. To test and evaluate as many operational radiosonde systems as possible at the same location and time.
2. To characterize the individual radiosondes with respect to their reproducibility and to determine the uncertainty of the different measured parameters.
3. To compare the different radiosonde systems to characterized reference systems employed in the GCOS Reference Upper Air Network (GRUAN).
4. To characterize measurement errors and uncertainties of radiosonde sensors under laboratory conditions.
5. To demonstrate the added-value of surface-based remote-sensing systems for upper-air measurements and to develop a methodology to compare the measurements of radiosondes with remote-sensing instruments.
To evaluate the capability of each system participating in the intercomparison to reach the uncertainty targets as defined in OSCAR.
Planning, location and organisation
The campaign will take place in 2021 at DWD’s Meteorological Observatory Lindenberg (Germany), and will be organized under the auspices of WMO, with DWD and MeteoSwiss as project co-leads and local organizers. The campaign will consist of two distinct parts, a laboratory campaign and a field campaign. The field campaign is scheduled for August-September 2021, whereas the laboratory campaign will take place around the fourth quarter of 2021 (December 2020-April 2021). During the field campaign, for each radiosonde model, approximately 15 daytime and approximately 15 night-time soundings will be performed. A key aspect of the project is the selection and application of reference in-situ instruments for temperature and water vapour, the characterization of radiosondes under laboratory conditions and the application of manufacturer-independent checks of the radiosondes prior to launch. Lindenberg Observatory has an extensive and unique collection of remote sensing instrumentation, which will be included in the campaign to assess and characterize the added-value of remote sensing instruments for upper-air measurements.
A Project Team will be established to organize and conduct the intercomparison, the data analysis, and the writing of the Final Report, according to the project plan approved by the corresponding WMO Management Group. The Project Team will be accountable to the corresponding WMO governance structure. MeteoSwiss and DWD had offered to co-lead the campaign and engaged themselves to cover a large part of the work. The Project Team will encompass the following functions:
Core team members:
- Project Co-Leaders
- Laboratory campaign manager
- Field campaign manager
- Database Manager
- Data analysis manager
- Remote-sensing systems manager
- Training Manager
- Aircraft-based observations provider
- Aircraft-based observation analyst
- Satellite observations lead
- Communication and environmental impact
- Numerical Weather Prediction
- Data analysis scientists
- Evaluation of applications
Description of the campaign site
The Lindenberg Meteorological Observatory is located in a rural environment approximately 65 km south east of Berlin, Germany's capital. The observatory was founded in 1905 by Richard Aßmann, and has a long and continuous track record of numerous and substantial contributions to research of meteorological observations. In its present state, the observatory covers four fields of research, in-situ sounding, remote sensing, boundary layer and radiation. It hosts a wide suite of instrumentation, both for operational and research purposes, and has extensive laboratory facilities for characterizing radiosonde sensors. Operational radiosoundings have been performed on a daily basis since 1947 without interruption, with a current balloon launch schedule of 4 times per day. Furthermore, Lindenberg is a GUAN and GRUAN site, and hosts the GRUAN Lead Centre. The site has extensive experience with launching large payload rigs for research purposes.
The goal of the laboratory tests is to characterize the most important measurement and calibration errors and uncertainties of the radiosonde's temperature and humidity sensors. This will help the Project Team in understanding and interpreting the results of the balloon sounding campaign. The benefit of the laboratory tests is that these provide an independent assessment of the errors and uncertainties, which is a valuable addition to the radiosonde intercomparison, which provides uncertainties/biases with respect to each other. Lindenberg Observatory has well-equipped laboratory facilities for testing and characterizing radiosondes under various conditions, ranging from typical surface conditions to those encountered at 35 km altitude. In the set-ups, relevant experimental parameters such as temperature, pressure, water vapor content, ventilation speed and actinic flux can be controlled and monitored, allowing for the investigation of the accuracy of the radiosonde’s sensors. The laboratory measurement data will be treated confidentially in view of the potential commercial and strategic sensitivity of these data for the manufacturers. In the Final Report of the campaign, the results of the laboratory measurements will be presented anonymously to ensure that these are not traceable to the respective radiosonde model.
Radiosounding field campaign
The radiosounding field campaign will last approximately four weeks from mid-August to mid-September 2021. The planning will allow that for each radiosonde model approximately 15 daytime and approximately 15 night-time soundings can be performed. The schedule incorporates multiple soundings per day. Routine radiosoundings in Lindenberg are performed at fixed times (0, 6, 12 and 18 UTC) but the soundings for the campaign are not bound to these times and can be scheduled as required. It is expected that the number of participating manufacturers will exceed the number of radiosondes that can be mounted on one rig. Therefore, the sondes will be distributed over 2 separate payloads/balloons that will be launched within several minutes of each other. The reference radiosondes will be part of each rig that is flown. The references will be selected by the Project Team, upon recommendation from the GRUAN Working Group, and will remain so for the duration of the campaign. The reproducibility (campaign goal #2) is tested by mounting two identical radiosondes on the same rig, so called double flights. A limited number of double flights for all radiosonde models will allow for the evaluation of the measurement uncertainty of these models. Prior to each sounding, the GRUAN-adopted practice of an additional manufacturer-independent ground check will be performed. This involves inserting the radiosondes in a Standard Humidity Chamber (SHC) with 100 %RH atmosphere and recording its readings for several minutes. Further GRUAN-involvement concerns the use of in-situ reference instruments, such as the cryogenic frostpoint hygrometer (CFH) for humidity measurements. It is proposed that the operation of the radiosondes and the receiving systems during the radiosounding field campaign will be performed by independent personnel recruited from WMO Members (see section on Capacity building of operational personnel below for more details).
Selection of participants
General rules for participation in the campaign are:
- The radiosounding system must be compatible with the infrastructure of the Lindenberg site.
- The manufacturer has to adhere to and sign the campaign’s data policy.
- It is expected that the radiosonde system has a minimum operational maturity and the campaign will not be used to test prototypes. Only 1 radiosonde model per manufacturer will be accepted.
- It is intended to give at least one new radiosonde manufacturer the opportunity to participate in the campaign.
- The selection criteria do not apply to radiosonde models that are used as working Reference.
In the case that the number of applications that meet the mandatory criteria exceeds the capacity of the Lindenberg Observatory, a selection assessment will be undertaken.
Remote sensing observations
The project co-leads recognized the potential and maturity of surface based remote sensing systems and commits to evaluate the fitness for purpose of such instruments. A full scale intercomparison is not feasible in the framework of the campaign because resources are not available next to the radiosonde intercomparison. Therefore, the remote-sensing activities will rely on the instrumentation which is already available at the Lindenberg Observatory and will perform an assessment of each technology rather than of specific models for a given technology.
The following ground-based remote sensing instruments are expected to be available at Lindenberg for the campaign in 2021 (no commitment):
a) 482 MHz radar wind profiler (RWP),
b) 1.5 μm Doppler lidar,
c) 355 nm multiparameter Raman lidar with spectroscopic capabilities,
d) Microwave radiometer,
e) Water vapour DIAL,
f) 35 GHz cloud radar,
On the one hand, additional information on the state of the atmosphere shall help to plan and schedule the radiosonde launches. Information about the vertical structure of clouds and aerosol layers would further complement the measurements of the kinematic and thermodynamic state of the atmosphere, possibly helping to assess radiation effects on the in-situ sensors.
On the other hand, the remote sensing instruments shall be evaluated in terms of their fitness for purpose to meet the user requirements defined in OSCAR, in the same way as the radiosondes. The focus will be put on the parameters horizontal wind vector, temperature and humidity.
It is expected that after the intercomparison, the data analysis software will be made available to Members to enable them to make robust comparisons when testing radiosondes during future procurement and selection processes.
Capacity Building of Operational Personnel
The operation of the radiosondes and the receiving systems during the radiosounding field campaign will be performed by independent personnel. The rationale for doing so is:
- to evaluate the user-friendliness and ease of operability of the radiosonde systems, which is a relevant factor in the procurement process for WMO Members,
- to enable an independent comparison of the radiosonde systems,
- to train staff from WMO Members in the operation of radiosonde systems with preference to staff from developing countries.
The operators of the radiosonde systems will be recruited from WMO Members as a form of capacity building. In case operators can't be recruited from WMO Members, DWD will provide the operators. The training of the operators on each radiosonde system will be performed by the manufacturer. The manufacturer will take responsibility for appropriate training and capacity building with their systems. Technical staff may be trained in the use of multiple systems (up to three) to be able to support more than one manufacturer.