Attached is a document describing the requirements for GRUAN station regarding the pre-launch procedures for routine soundings with Vaisala RS92 radiosondes. In order to obtain high data quality, ensure long term stability, and to make sure that measurement uncertainties are within the ranges that are reported in the product files, it is important that some ground checks are made before launch in the way described in this document and that the meta-data are reported to the GRUAN lead centre.
The paper “A guide for upper-air reference measurements” by F. Immler, J. Dykema, T. Gardiner, D. N. Whiteman, P. W. Thorne, and H. Vömel went online on the interactive Journal “Atmospheric Measurement Techniques” where it is open for public discussion for eight weeks (link).
The following paragraphs from an e-mail by John Dykema describes how co-location and coincidence could be formalized. As an example, the measurements of a temperature profile by a sensor on a balloon and a profile retrieved from microwave radiometry are assumed.
Once we have two well-characterized sensors with rigorously assessed and validated uncertainties, then we can make robust recommendations on co-location.
The measurement uncertainty will be established by analysing all sources of measurement uncertainty and by combining them to one single error bar for each measurement point. The investigation of all sources of uncertainty will be a time consuming and iterative process and will require a detailed understanding of the instrumentation that is being used as well as a careful consideration of the operational influences that contribute to the measurement uncertainty. Error bars during the early stages of GRUAN are expected to be somewhat crude. As the understanding of the instrumentation improves and as the instrumentation itself improves, uncertainty estimations are expected to improve as well. Thus, it is expected that there will be different versions of GRUAN data, which differ mostly in their uncertainty estimate.
Franz Immler wrote:
During the Lindenberg meeting it was agreed that among other things GRUAN station were required to conduct
1 x weekly production radiosonde with the best technology currently available (GCOS-121)
this suggestion has already often been argued about and is certainly one of the weaker points in the current concept of GRUAN. It obviously refers to an commercially available standard radiosonde which is currently launched at most sites 2 or even 4 times a day anyway. Even though some plans referring to extended ground check and alike are being discussed, it is currently not clear what should be the benefit of the additional launch of such an instrument.
What I suggest therefore, is to launch (at least) once a week two different high quality radiosondes on one balloon. Every GRUAN station can select one additional type of radiosonde to what they regularly start anyway and conduct a parallel launch of the two radiosondes once a week, better twice a week, one day and one night time. In principal every station can choose any radisonde they like but it is recommended to seek guidance from the lead centre.