1、 STD*CEPT ERC REPORT 41-ENGL 1976 I 2326414 O015557 TU3 I ERC REPORT 41 v European Radiocommunications Committee (ER0 -.- within the European Conference of Postai and Telecommunicati&.s Administrations (CEFT) TECHNICAL AND OPERATIONAL CHARACTERISTICS OF WEATHER RADIOSONDES IN EUROPE Rome, October 19
2、96 Copyright 1996 the European Conference of Postai and Telecommunications Administrations (CEPT) STDnCEPT ERC REPORT 43-ENGL 1996 2326434 0035557 886 ERC REPORT 41 Page 1 TECHNICAL AND OPERATIONAL CHARACTERISTICS OF WEATHER RADIOSONDES IN EUROPE 1. INTRODUCTION This paper is intended as a comprehen
3、sive response to the recommendations in DSI Phase II that affect the radiofrequency spectrum available for weather radiosondes in Europe. The relevant recommendations are listed in detail in Annex A. 2. USE OF RADIOSONDES Radiosondes are lifted by weather balloons to heights from 20 to 35 km. The ra
4、diosonde will be often carried more than 100 km from the launch site before falling to earth and on some occasions more than 300 km from the launch site when upper winds are strongest. Therefore, most radiosondes are treated as disposable and are used only once. In order to keep operational costs to
5、 a minimum, the radiosonde design is kept as simple as possible within the constraints of achieving the necessary standards of measurement accuracy. Data processing and storage on the radiosonde are kept to a minimum with measurements transmitted in red time to the ground station receiver. Thus, suc
6、cessful operation of all modem radiosonde systems relies on essentially uninterrupted communication between the radiosonde and its ground receiver. 21. Daily Meteorological Operations Radiosondes are mainly used for upper air measurements from the surface up to altitudes of between 20 and 35 km of t
7、he meteorological variables: pressure, temperature, relative humidity, wind speed and direction. More than 15 radiosondes per year are launched for this purpose in Europe and western Russia. The radiosonde measurements are vital to national weather forecasting capability (and hence severe weather wa
8、rning services for the public involving protection of life and property). The measurements are mostiy performed routinely at 00 and 12 UTC, but in some countries in Europe where significant changes in weather are common the separation between measurements is reduced to 6 hours. For specific research
9、 into severe weather, time separations as low as 3 hours may be used over large areas of Europe for several days. The launch times actually fail withii a window of about 3 hours, with the Window starting about 45 minutes before the nominal time. The launch may be up to 2 hours late if the initial ra
10、diosonde fails in flight. The radiosonde will usually transmit for about 3 hours in total during preparation, flight and falling to earth after balloon burst. The majority of the criticai information for weather forecasters is contained in the detail of the variation of temperature, relative humidit
11、y and wind speed and direction in the vertical. The radiosonde systems are the only meteorological observing system able to reguiarly provide the vertical resolution that meteorologists need for ail four variables. Accurate measurement of the height where a discontinuity in a variable OCCUTS is vita
12、l. Such features often occur shortly after launch, for example the height of fog top, cloud base or the top of the atmospheric boundary layer. Uninterrupted communication between the radiosonde and the ground station is essential if the necessary measurement accuracy is to be sustained. Radiosonde o
13、bservations are considered essential to maintain stability in the World Meteorological Organisation (WMO) Global Observing System. Successful derivation of vertical temperature structure from satellite sounding measurements requires a computation initialised either directly from radiosonde statistic
14、s or from the numerical weather forecast itself. In the latter situation, the radiosonde measurements ensure that the vertical structure in these forecasts remains accurate and stable with time. Thus, radiosonde observations are expected to remain absolutely necessary for meteorological operations f
15、or the foreseeable future. STD-CEPT ERC REPORT 4L-ENGL 1996 232b414 0035560 5T8 = ERC REPORT 41 Page 2 2.2. 2.3. 2.4. 3. 3.1. Monitoring Climate Change Large world-wide changes have occurred in atmospheric temperature and ozone in the last 20 years. Many of the largest changes have occurred at heigh
16、ts between 12 and 30 km above the surface of the earth. The changes are large enough to cause concern about safety of future public health. The routine daily radiosonde observations to heights above 30 km identify the vertical distribution of the temperature changes that occur and hence the causes o
17、f the changes can be evaluated. In addition, ozonesonde measurements to Similar heights determine the vertical distribution of the ozone depletion that now appears to be occurring in northern Europe in winter and spring. In many cases, radiosondes and ozonesondes flown in winter in northern Europe w
18、ill encounter very strong upper winds. Good communications between radiosonde and ground receiver are essential under these circumstances when slant ranges may exceed 200 lan and balloon elevations may be well below 10 at upper levels towards the end of a flight. Successful sampling of climate chang
19、e requires the use of radiosondes with established systematic error characte ristics. The requirement for continuity in the the series of upper air measurements world-wide means that new radiosonde designs are only introduced into operation after several years of intensive testing, both in the labor
20、atory and in the free atmosphere. Defence use Radiosondes are used in significant numbers for military operations in most countries in Europe. The radiosonde use by the military does not usually duplicate the civilian weather forecasting operations. Upper ah- measurements are essential to the accura
21、cy of modan artillery and rocket operations, as weli as safety and noise control at military ranges. The military use is not decreasing with time, since with dem automation it is now much easier to successfully operate mobile battlefield systems and shipboard systems without highly skilled operators
22、 and a large amount of supporting equipment. The number of radiosondes used by the military on average is probably up to one third of those used for civilian operations. Civilian radiosonde operations have to accommodate the military use and this expands the radiofrequency spectrum required for radi
23、osonde operations. This is particularly critical when military launch sites are within 150 km of the civilian launch sites. Other Civilian Users Additional radiosonde systems are operated independently of the main civilian meteorological organisation by national research institutes. Specific investi
24、gations will include environmental pollution, hydrology, radioactivity in the free atmosphere, significant weather phenomena (e.g. winter storms, thunderstorms, etc.) and oceanography. In some areas of Europe there will be negligible additional use. However, in other areas it has been found that add
25、itional users are operating for up to 20 per cent of the time when the main civilian operations are in progress. RADIOFREQUENCY USED FOR RADIOSONDE OPERATIONS Choice of Met-aids band In Europe and Western Russia there are about 214 radiosonde launch sites that report information daily to all the oth
26、er meteorological services worldwide through the WMO Communications network. Of these stations, 11 1 use the Met-aids band centred at 403 MHz, 11 use the Met-aids band centred at about 1685 MHz and 92 stations in Russia or associated states use equipment operating at 1780 MHz. At this time 403 MHz r
27、adiosondes are primarily used by CEPT Members. The radiofrequency characteristics of the 403 MHz radiosonde systems are sdsed in Annex B. The low power output of radiosondes is dictated by the capability of the batteries that can safely be flown without endangering public safety. 403 MHz has been ch
28、osen for radiosonde operations for the two following reasons: ERC REPORT 41 Page 3 (i) in many countries in north-west Europe average upper winds are often very strong for prolonged periods during the year. The better signal reception at 403 MHz than at 1680 MHz for very long ranges and low elevatio
29、ns allows satisfactory radiosonde operations to the longest ranges encountered. 403 MHz radiosondes with navaid windfinding (either Loran-C or GPS) or used with independent tracking from a primary radar are essential for accurate winds when average upper winds are very strong. This is because radiot
30、heodolite systems that rely on passive tracking of radiosonde direction by the receiving aerial have great difficulty in measuring elevation with sufficient accuracy at low elevations to provide reliable winds. (ii) puily automated ground systems have reduced radiosonde operational costs across Euro
31、pe in the last decade. The most common fully automated system operates at 403 MHz and relies on Omega navaid signals for windfinding. The Omega system will be closed within a couple of years. At stations where very strong upper winds are rare, a choice will have to be made between a radiotheodolite
32、at 1685 MHz or the more accurate GPS windfinding at 403 MHz. A radiotheodolite has high initial capital cost and requires more staff for operations and maintenance. The GPS radiosondes will be more expensive than those for radiotheodolite operations. in most of Europe, upper winds are strong for par
33、t of the year. Thus, most countries using Omega windfinding will have to change to GPS windfinding at 403 MHz. Thus, it is impossible for most countries in Europe to move to using 1685 MHz for weather radiosonde operations and Recommendation 39 of DSI Phase II must be rejected as impractical. 3.2 Ra
34、diofrequency occupancy required for radiosonde operations In some parts of Europe, the radiosonde stations operated by the national meteorological service are spaced about 500 km or further apart and there is negligible additional radiosonde use by the military or other researchers. in this situatio
35、n, even with radiosonde transmitters at 403 MHz that may drift by about 500 kHz during flight, successful radiosonde operations oniy requires two or three frequencies each separated by about 1 MHz at most. in several countries, this situation has been exploited by the national radiocommunication aut
36、horities by restricting radiosonde operations to only part of the Met-aids band and utilising the remaining spectrum for defence and commercial applications. The current allocation situation needs to be carefully reviewed before planning future radiofrequency allocations in the Met-aids bands. Howev
37、er, in many densely populated areas of Europe the spacing of the stations operated by the national meteorological services is close to 300 krn, the optimum recommended by the World Meteorological Organisation. This is necessitated by the large variability in weather experienced by north-west Europe
38、(variable both in time space) for most of the year. There are also many military stations at distances less than 150 km from the civilian stations as well as many additionai users. In this situation, radiosonde observations from one site will interfere with the other sites unless strict radiofrequen
39、cy management is adopted. Interference will be particularly bad in winter when the radiosondes may travel in excess of 300 km before falling to the ground. In this situation, the main national radiosonde operators are already using radiosondes with relatively stable transmitters, (stable to better t
40、han f 5 kHz in Germany, stable to better thank 100 kHz during flight in the UK). STD-CEPT ERC REPORT 41-ENGL 197b 232b414 00155b2 370 = National civilian meteorological service, station spacing 300 km *8 stations Defence use at range stations or mobile systems interspersed between civilian stations
41、*at least 8 stations + mobile systems exploiting time share of channels Other additional users at least 10 systems, Data Collection platforms, uplink to meteorolo- gical satellites at least 100 sites, time share of JCRC REPORT 41 Page. 4 2 MHz 2 MHz 1MHz 0.5 MHz Table 1 summarises the spectrum occup
42、ancy required by the radiosonde users at present in countries where very stable transmitters are in use. This suggests that there is little scope for a reduction in the size of the Met-aids allocation at 403 MHz. If sharing is to be increased in future, then it should be with systems that are able t
43、o operate with the radiosondes without cschannel interference. There is little room for band segmentation and adjacent channel sharing. 4. 4.1. User Width of radiofrequency spectrum required between 400.15 and 406 MHz Table 1 Radiofrequency spectrum for Met-aids and meteorological satellite operatio
44、ns in north-west Europe with radiosondes using high stability transmitters at 403 MHz * Each main station requires at least two independent frequency allocations to cope with crash launches and repeat fights Some military stations require 3 or 4 frequencies to aliow radiosondes to be launched at 30
45、minute intervals * POSSIBILITIES OF SHARING WITH OTHER PRIMARY USERS In those countries where the radiosonde stations are separated by large distances there is clearly scope for national agreements so that radiosonde operations share with other services within the band fi-om 400.15 to 406 MHz. DSI P
46、hase II proposes sharing with a general low power device band (Recommendations 28,29 and 35) and also possibly with the Mobile Satellite Service (Recommendation 38). WMO will also propose at WRC-97 that the Meteorological Satellite services, earth to space links, should be raised to primary status f
47、iom 401 to 403 MHz. Meteorological satellite services (earth to space links from data collection platforms) The possibilities of Co-channel sharing between Data Collection Platform (DCP) uplinks to meteorological satellites and radiosonde operations are to be studied by WMO. Most DCPs in Europe curr
48、ently operate at frequencies between 401.6 and 402.2 MHz with transmitted power in the range 5 to 50 watts depending on the antenna available. There is no evidence to suggest that radiosonde operations interfere with DCP reception. DCPs transmitting close to radiosonde ground systems do cause interf
49、erence to radiosonde reception. However, this problem is usually managed by ensuring that DCP transmissions are short and take place at time during flight when a short radiosonde data loss is less critical. The Meteorological Satellite operators require that a theoretical study of interference from radiosondes be completed before agreeing to Co-channel sharing with radiosondes. Co-channel sharing between DCP and radiosonde operations may be possible in some countries. STDoCEPT ERC REPORT 4L-ENGL Lqqb ERC REPORT 41 Page 5 4.2. Low Power Devices For a low power device to
