User Survey 2006 Results[reference number for survey report: SAF/GRAS/DMI/MGT/US2/001]
Of 503 transmitted emails 115 unique replies were eventually received.
The results indicated a wide interest in RO-based data with responses both from technical people involved in the GPS missions now being planned and awaiting launch at the moment of writing, and from the broader meteorological and climate research community. The results can be summarized in many ways. An overview of the actual classes of answers is given next, where the text of the questions have been paraphrased. Answer frequencies are given in percent of all answers to the particular question.
The number of answers to each question varied from 138 (question 2) to 51 (Questions 13 and 14).
From the UQ results and the distribution of answers we can summarize the results: Most responders were in the atmospheric sciences and engineering, and would like to use RO data as soon as it becomes available. Refractivity profiles alone will be wanted by half, and most want access to both profiles and gridded data. Data resolution in gridded data is most useful if high particular with high resolution in time. Non-numeric data representations would be useful but not used for primary science purposes. Uncertainty estimates would be used by nearly all responders, as would meta-data and access to a help-desk function, whereas a data-manipulation page on the internet was judged useful but not essential by most users. By far most users want access to data in ASCII format while the preferred packeted formats were NETCDF and GRIB. There was no real clear favourite choice for the level of data most requested, with all levels being indicated by some responders most did want level 2 data.
The last two questions were directed more at the expert level, and allowed for individual comments. Important points were made regarding possible pit-falls in the generation of gridded climate data. If studies of climate-change is to be possible with RO-based data, then biases generated from sampling in time and space require special attention. When multiple GPS satellites are in place in space and are used for RO work, this problem will be less acute, but during operations with a few satellites attention should be focused on the effects due to the time of day when profiles fall in a certain region the time of day may drift during the year and therefore monthly or seasonal averages may be biased. Comments were also received on the potential community of users of RO data, and it was evident that the call for high resolution RO-based data came from people working with local surface processes, such as evaporation. In the future, when many systems deliver RO data, products with simultaneous high spatial and temporal resolution will be possible and will have an audience in that community.
BACKGROUNDOccultations of the radio signals from GPS satellites can provide detailed information about the atmosphere. The data consist of high-resolution vertical profiles of atmospheric quantities like temperature, pressure, specific humidity and refractivity, from (near) the surface up to the upper stratosphere. The vertical resolution will be in the range 150-300 m, and radio occultation (RO) profiles have been demonstrated to contain a very high information content in the upper troposphere and lower stratosphere. Such RO data will soon be available from EUMETSAT's Metop satellite, which will give about 500 vertical atmospheric profiles per day evenly distributed across the globe, and from the COSMIC satellites giving about 3000 vertical atmospheric profiles per day.
RO METHOD & BENEFITSThe basic principle of the RO method is that a receiver onboard a low-orbiting satellite tracks GPS signals as the transmitting satellite sets or rises behind the Earth. Due to refraction in the ionosphere and the neutral atmosphere the signal is delayed and its path bent, enabling calculation of profiles of the index of refraction (or refractivity) and subsequently temperature and humidity as a function of height. Many of the characteristics of RO data suggest them as a near- ideal resource for climate studies, particularly the global coverage, the all-weather capability, and the self-calibrated nature of the RO data. The latter property - which distinguishes RO from most other satellite observational techniques - allows for relatively easy inter-comparison of data from different satellites and RO instruments, which is required to construct long time series covering many years and even decades. The EUMETSAT Polar System (EPS), with its planned series of three Metop satellites, now provides an opportunity to create RO occultation based climatologies of high quality on a longer term. This will help us meet the requirements of both the scientific community and a wide range of climate data users. For these purposes, we are currently undertaking studies on how to best exploit the GRAS data from a climate perspective.
THIS QUESTIONNAIREThe GRAS SAF is part of EUMETSAT's network of Satellite Application Facilities (SAFs). The objective of the GRAS SAF is to deliver operational RO products from the GRAS instruments onboard the three Metop satellites. The GRAS SAF will enter into the operational phase and deliver products from around the beginning of 2007. In the GRAS SAF project we now need to determine the interest in climate data derived from RO profiles, and what form the data should have. Hence, this questionnaire tries to build a picture of the priorities of potential climate data users. Because the users of RO data will be from a wide range of fields, with different levels of interest and expertise, we divide the survey into three parts. You may skip the last part if you are not familiar with the RO technique.
If you are not familiar with the radio occultation principle, you may want to read this short introduction.