1、STD*ITU-R RECMN P*LLqB-L-ENGL 1997 W -I855212 0530820 T78 Rec. ITU-R P.1148-1 1 RECOMMENDATION ITU-R P. 1 148-1 STANDARDIZED PROCEDURE FOR COMPARING PREDICTED AND OBSERVED HF SKY-WAVE SIGNAL INTENSITIES AND THE PRESENTATION OF SUCH COMPARISONS* (Question ITU-R 22213) (1 995- 1997) The ITU Radiocommu
2、nication Assembly, considering that the overall accuracy of prediction procedures needs to be assessed; that the effect of proposed changes to prediction procedures needs to be determined; that detailed information regarding the modal, spatial, temporal and related accuracies will assist with the a)
3、 b) c) future development of such procedures, recommends that the following procedure given in Annex 1 be adopted for the comparison of predicted and observed HF that such comparisons be presented in the manner shown in Annex 2. 1 sky-wave signal intensities; 2 ANNEX 1 1 Introduction The method desc
4、ribed is a standardized procedure for comparing predicted and observed sky-wave signal intensities at frequencies between 2 and 30 MHz. Such comparisons provide information on the accuracy of prediction methods and on desirable improvements to them. It is important that administrations and organizat
5、ions keep the 1TU-R informed on the current status of their comparisons. Some sample results of comparisons are contained in this Recommendation. 2 General In order to obtain comparable results, the same data set and the same procedure should be applied when making comparisons between predicted and
6、observed signal intensities. The most recent data base should be used. This is an ITU-R-agreed data set and provides a wide range of observations with respect to distance, month, sunspot number, frequency and geographical zone. The output from the comparisons should be: - count, - mean difference (d
7、B), - standard deviation (dB). “Count” indicates the number of samples used in the comparisons. The “mean difference” provides a measure of the deviation between predicted and observed monthly median signal intensities. The most important parameter for assessing the accuracy of the monthly median si
8、gnal intensities given by a particular prediction method is the standard deviation (see equations (I) and (2) but it should be noted that this provides no information about the accuracy on individual days. * A computer program associated with the procedure described in this Recommendation is availab
9、le; for details, contact the ITU Radiocommunication Bureau. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services STD-ITU-R RECMN P.114B-L-ENGL 1777 4855212 0530821 724 2 Rec. TU-R P.1148-1 In order to find systematic deviations (e.g. as a
10、function of distance or geographical zone) of a particular prediction method, comparisons should be made for a variety of different subsets or combinations of subsets of data. The purpose of the detailed subsets of comparisons is to give hints for the detection of systematic weaknesses of the method
11、 under consideration. The choice of a certain prediction method should not be based on favourable results obtained for a particular subset (e.g. distance range). 3 Different comparisons, .e. the calculation of mean difference and standard deviation (see Annex 2), should be made for the following par
12、ameters: Subsets for which comparisons should be made 3.1 Frequencies,f - single frequency, - - frequency groups: all frequencies of the same circuit, I f I 5MH 60“ 3.4 Sunspot numbers, R12 COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Servi
13、ces3.5 Season (at path midpoint) November, December, January, February I Season Month I 1 Northern Hemisphere Southern Hemisphere Winter Summer May, June, July, August September, October I March, April I Spring I Autumn I Summer Winter Autumn Spring 3.6 Local time h (at path midpoint) Intervals of 1
14、 h throughout the 24 h; e.g. O0 - mean difference = n where: p : predicted rn : measured n : count. V n-1 - standard deviation = Table 2 provides an example of the type of output produced by the comparison computer program. 4.3 Graphic representation In the histograms in Figures 1 and 2, columns of
15、5 dB are generated (e.g. -2.5 to 2.5 dB, 2.6 to 7.5 dB, 7.6 to 12.5 dB .) in the range -32.5 dB to +37.5 dB. Each subset listed in 5 3 should be accompanied by a histogram. 4.4 Measures to be taken if a prediction does not give the median signal intensity for all days of the month In some cases wher
16、e predictions give the median signal intensity only for a certain “fraction of days” per month (expressed as a percentage (see 4.1 c), the measured and predicted values cannot be compared directly. Only when the fraction of days is at least 99% are the measured and predicted values directly comparab
17、le. In all other cases a conversion procedure must be applied to the measured values. If the fraction of days is, for example, 50%, proper ionospheric reflection occurs on 15 days of the month and the predicted median signal intensity is valid for those I5 days only. The prediction does not give any
18、 information on the signal intensity on the other 15 days of the month. A measured monthly median, however, is derived from 30 daily values (including the 15 days without proper reflection). Consequently, the measured monthly median is likely to be lower than the predicted median. If a data bank con
19、tains all daily values the measured value corresponding to the predicted fraction of days can be derived by determining the median value for the predicted fraction of days. (Note that Data Bank DI does not contain daily values.) The following procedure describes how the measured (30 day) monthly med
20、ian signal intensity can be converted to the same fraction of days per month as that given for the predicted signal intensity: Step i: Calculate thef/(path basic MUF) ratio. Skp 2: If the data bank does not contain deciles (Data Bank DI does not) take the measured value as the 50% value and calculat
21、e 10% and 90% values by means of Table 1. This table requires information about the ratio f(path basic MUF) and whether or not the great circle path crosses the 60” corrected geomagnetic latitude (north or south). The actual ratio should be interpolated linearly between the values contained in the t
22、able. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesRec. TU-R P. 1 148-1 5 Corrected geomagnetic latitude() TABLE I = - .i= I I wherey, i = 1,2, N, NI 3 1, are the daily samples of the measured quantity. Step 3: respectively, the mea
23、n M(z), variance V(z) and standard deviation S(z) of the difference z = x -y are calculated by: Given the monthly means M(x), MO.), and variances V(x), Vb), of the predictions and measurements, and: Given the means M,(z), variances b(z) and numbers of samples NJ for an individual month j, the mean M
24、(z), variance V(z) and standard deviation S(z) of a subset of values including a range of m months are calculated by: tn 1 CNj-l V(2) = m j=i 1 j= I L and: COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesRec. ITU-R P.1148-1 ANNEX 2 TAB
25、LE 2 An example of the tabular output produced by the comparison computer program I I Subset Frequency groups (MHz): 2- 5 5-10 10-15 15-30 Distance (krn): o- 999 1000- 1999 2 000- 2 999 3 000- 3 999 4 000- 4 999 5 000- 6 999 7 000- 8 999 9 000- 1 1 999 12 000- 14 999 I5 000-1 7 999 I8 000-21 999 22
26、000-40 O00 Geomagnetic latitude (degrees) at path midpoint: 0-20 20-40 40-60 60 Sunspot number: O- 14 15- 44 45- 74 75- 104 105-149 149 Season: Winter Spring Summer Autumn Local time at path midpoint (h): 00-04 04-08 08-12 12-16 16-20 20-24 Origin of data: Germany Japan China India Deutsche Welle BB
27、CIE B U Australia All data: Count 4 030 4 004 5 270 2 964 6 439 I144 151 975 I26 2 785 59 2 223 607 1093 O 666 2 806 5 120 6 226 2116 1333 5 229 2 969 2 121 2 789 1827 3 919 4018 4 165 4 166 2 557 3 165 3 182 2 955 2 228 2 181 I O 499 4119 428 I82 783 161 96 16 268 Below and above MUF Mean differenc
28、e (dB) -1.7 -0.3 -0.4 3.7 -0.3 1.5 o. I 3.8 1 .o -1.2 -0.9 -1 .o I .2 3.4 0.0 -2.0 1.5 -0.5 -0.3 0.3 I .2 2.5 -0.5 -3.4 -I .5 -0.7 0.6 0.3 -0.4 -0.2 -0.6 0.8 0.9 0.3 -1.6 -0. I 1.1 -2.3 1.4 -2.2 -1.4 -0.4 -0.7 0.0 Standard deviation dB) 9. I 10.6 9.9 12.1 7.1 7.4 6.9 13.6 7.4 14.5 7.3 11.1 9.6 9.2 0
29、.0 12. I 10.7 8.9 9.0 16.0 9.7 10.3 10.3 10.8 9.9 10.4 11.2 10.5 9.7 10.4 11.2 9.7 9.8 10.0 10.6 11.6 11.4 7.5 7.7 9.0 10.0 10.7 5.9 10.5 7 COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesSTD-ITU-R RECMN P.LL48-L-ENGL 1797 4855212 0530
30、827 342 9 Rec. ITU-R P. 1 148- 1 FIGURE i An example of a histogram of predicted versus measured field strength produced by the comparison computer program 4 O00 3 500 3 O00 2 500 * 5 2000 o i 500 i O00 5 O0 O -30 -25 -20 -15 -10 -5 O All data below and above MUF: Count: 16 268 Mean difference: 0.0
31、dB Standard deviation: 10.5 dB I i i IO 15 I 20 25 30 35 1148-01 Previous page is blank COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services10 1 O00 900 800 700 600 * % 500 u 400 300 2 O0 1 O0 O FIGURE 2 A further example of a histogram of
32、 predicted versus measured field strength produced by the program -30 -25 -20 -15 -10 -5 O All data for frequencies above MUF: 10 15 I- 20 25 30 35 Count: 4 707 Mean difference: 3.0 dB Standard deviation: 11.7 dB 1148-02 COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services
