1、Rec. ITU-R S.1339-1 1 RECOMMENDATION ITU-R S.1339-1* SHARING BETWEEN SPACEBORNE PASSIVE SENSORS OF THE EARTH EXPLORATION-SATELLITE SERVICE AND INTER-SATELLITE LINKS OF GEOSTATIONARY-SATELLITE NETWORKS IN THE RANGE 54.25 TO 59.3 GHz (Question ITU-R 246/4) (1997-1999) The ITU Radiocommunication Assemb
2、ly, considering a) that Resolution 643 (WRC-95) of the World Radiocommunication Conference (Geneva, 1995) (WRC-95) instructed the ITU-R to carry out the necessary studies to identify the bands most suitable for the inter-satellite service (ISS) in the frequency range from 50 to 70 GHz in order to en
3、able the World Radiocommunication Conference (Geneva, 1997) (WRC-97) to make appropriate allocations to that service; b) that WRC-97 considered the allocation of frequency bands above 50 GHz to the Earth exploration-satellite service (EESS) (passive); cl that, as a result of WRC-97 decisions, the fr
4、equency bands 54.25-58.2 GHz and 59-59.3 GHz are currently shared on a co-primary basis by the EESS (passive), the space research service (SRS) (passive) and the ISS; d) that this unique band is important to passive measurements and sharing between the passive sensor space stations and space station
5、s in the ISS should be considered; e) that planned use of the ISS in the frequency bands near 60 GHz has increased significantly; f) that the technical characteristics and operational requirements of the ISS in these bands are identified in Recommendation ITU-R S .1327; g) that Recommendation ITU-R
6、SA. 1029 contains interference protection criteria for passive sensors in bands near 60 GHz; h) that studies have been conducted into the feasibility of sharing between spaceborne passive sensors and inter-satellite links (ISL) of geostationary-satellite networks, based on the protection criteria re
7、ferred to above, as detailed in Annex 1; j) that studies have concluded that non-geostationary orbit (non-GSO) ISS systems are likely to cause harmful interference to the passive sensors and that, in general, sharing is not feasible; k) that effective sharing between passive sensors and GSO ISS syst
8、ems will provide for maximum use of the spectrum, recognizing that there is a need for continued operation of existing and planned ISS systems in the band 56.9-57.0 GHz, that, based on the sharing studies contained in Annex 1, WRC-97 decided to adopt No. S5.556A of the Radio a) and that studies have
9、 shown these systems would not cause unacceptable interference into EESS (passive) sensors; b) Regulations (RR), recommends 1 flux-density (pfd) limit given in RR No. S5.556A. that Annex 1 be used in the design of GSO ISS networks in order for them to comply with the power * This Recommendation shou
10、ld be brought to the attention of Radiocommunication Study Group 7. 2 Calibration antenna pattern Calibration antenna back lobe (dBi) Rec. ITU-R S.1339-1 ANNEX 1 ex-CCIR Report 558 ex-CCIR Report 558 -10 -10 1 Introduction Calibration antenna diameter (m) Calibration antenna gain (dBi) This Annex co
11、ntains summaries of sharing studies, and methods for computing the sharing conditions between passive sensors of the EESS and geostationary systems of the ISS. The information was developed based on Recommenda- tions ITU-R SA.1028 and ITU-R SA.1029. However, as these Recommendations are revised, thi
12、s study should be reviewed for potential changes in the conclusions. 0.15 0.133 36 35 2 Assumptions Planned passive sensors operate in sun-synchronous near polar orbits (inclination - 99“), at altitudes below 1 O00 km. Frequency (GHz) Inclination (degrees) 2.1 Sensor assumptions 54.25 54.25 98.7 98.
13、7 2.1.1 The advanced microwave sounder unit (AMSU) sensor Calibration angle range (degrees) Planned calibration angle (degrees) The AMSU sensor is planned for operation in the near future, with parameters as in Table 1. The AMSU sensor scans the surface of the Earth in sensing mode. The scanning is
14、normal to the velocity vector, and through nadir (see Fig. 1). In calibration, the sensor takes a reading from space, away from the sun. The calibration angle can range between 65“ and 85“ away from nadir. The figure 83.3“ is assumed in this example. 65-85 To be determined 83.3 To be determined TABL
15、E 1 Sensor assumptions I Item I AMSU Sensor I Pushbroom Sensor I 6 304 I I Period (s) 6 304 I 833 I I Altitude (km) 833 -166 I I Interference threshold (dBW in 100 MHz) I -161 I 0.01 I I Time for interference (%) 0.01 Rec. ITU-R S.1339-1 3 FIGURE 1 Passive sensor scanning plane eTm Pitch axis Roll a
16、xis i Yaw axis a: AMSU scanning angle (+ 48“) : AMSU calibration angle (83.3“) The calibrations are all normal to the roll axis, and the locus of calibration vectors form a cone. The axis of the cone is tilted out of the equatorial plane by an amount equal to i - 90, where i is the inclination angle
17、 (degrees). The AMSU sensor antenna pattern is shown in Fig. 2. The pattern used in this analysis has been modified to provide for a -10 dBi back lobe, in accordance with the sensor design. This change makes no difference in the analysis, as back lobe coupling with GSO ISS has been shown not to caus
18、e interference. FIGURE 2 Sensor calibration antenna patterns O - 10 h F4 v g -20 .3 Y a :a -30 3 .3 n - 40 - 50 lo- 1 10 lo2 Off axis angle (degrees) AMSU sensor - pushbroom sensor 2.1.2 The pushbroom sensor 1339-02 Recommendation ITU-R SA.1029 contains the value of -166 dBW per 100 MHz as the permi
19、ssible interference level for pushbroom sensors. As is the case for a scanning sensor, the most severe interference configuration that must be examined is for the calibration mode when the sensor is directed at cold space and interference can be coupled into the main beam of the sensor antenna. 4 Re
20、c. ITU-R S.1339-1 The AMSU scanning sensor uses a common mechanically rotating antenna for both sensing of the atmosphere and for calibration. Thus, the main beam gain of this high-gain (36 + h2 km The distance R from the GSO ISL transmitter to the point on the sensor sphere closest to the ISL is: R
21、 = Jz2 + b2 km and the off-axis angle from the GSO ISL transmitter is: 8 = tg-l (db) degrees Rec. ITU-R S.1339-1 AC? (degrees) 11 150 The pfd calculated at the sensor sphere at latitude h is therefore given by: h (degrees) rGSO (km) P + G(8) - 10 log(4n(R x 1000)2) P + G(8) - 20 log R - 71 pfd = P +
22、 G(8) - (20lg R + 2010g1000 + 10lg4n) dB (W/rn2) in 100 MHz I 49.0 42 164 where G(B) is the off-axis gain of the GSO ISL transmitter antenna. Table 6 shows the results of a sample calculation. Maximum gain (dBi) G(0) (dB) TABLE 6 pfd calculation 58.5 See G (u/) in Rec. ITU-R S.672, Annex 1 R (km) 41
23、 502 I 2 I 0 (degrees) G(0) (dB) I I I P (dBW in 100 MHz) 2.8 11.1 8.2 pfd (dB(W/m2) in 100 MHz) -152.3 3.4 One of the inputs to the previous methodology on pfd calculation is h, the latitude of the spacecraft when pointing at the GSO arc. This methodology provides the necessary angle h. A passive s
24、ensor in low-Earth orbit needs to perform a cold space calibration. It accomplishes this task by pointing its antenna away from the Earth and sun, at an angle a with respect to the plane of its orbit. The problem occurs when the combination of calibration angle a and position in the sensor orbit cau
25、ses the calibration path to intersect the GSO arc. The goal of this test is to find, for a given geometry, the locations in the sensor orbit where this can occur. Given: Methodology to compute the latitude of sensor when pointing at the GSO arc r,. : the radius of the sensor orbit i,. : the inclinat
26、ion of the sensor orbit iGS0 : the inclination of the GSO plane cp : the sensor calibration angle rGS0 : the radius of the geostationary orbit find h, the latitude of the sensor when calibration can intersect the GSO arc. 12 Rec. ITU-R S.1339-1 The calibration is always directed at a point C as indi
27、cated in Fig. 10. FIGURE 10 Geometry for calculating sensor latitude Sensor orbital plane The distances and angles are found by the method below. FIGURE 11 Sensor latitude angle “sens. dl = - cos cp d, = dl sincp d3 = r GSO cos(isenss. - 90“ - iGso) d, = r sin(isens, - 90“ - iGso) GSO d3 - d2 w = 18
28、0“ - (90“ + a) d, = d, (sin alsin W) d, = d, cos(isenss. - 90“) Rec. ITU-R S.1339-1 Now solving for the angle y, as in Fig. 11 x = r sin y y = d6 22 2 r sin y d6 - +-1 a0 bU where: and r is as shown in Fig. 11. By substitution: d6 rsens. COS (isens. - 9oo)i2 22 2 r sin y rsens. =I- Since: 2 2 2 22 r
29、2 = d6 + x = d6 + r sin y r2 = d6 (i - sin2 y) Therefore: 1 2 2 - rsens. - - sin y 2 2 1 - sin y d; cos (isens. - 90) 1 2 2 rsens. tg y=- 2 di cos (isens. - 90) 13 1 cos (isens. - 90) 2 y = tg-l - 2 h = 90“ - y 14 Rec. ITU-R S.1339-1 Table 7 shows the results of a sample calculation. Sensor inclinat
30、ion (degrees) TABLE 7 Sample latitude calculation 100.1 Sensor altitude (km) Calibration angle (degrees) 1 O00 70.0 GSO inclination (degrees) Latitude where sensors main beam intersects the GSO arc (degrees) 2.0 49.0 3.5 pfd at altitudes less than 1 O00 km The discrimination from a typical ISS GSO s
31、ystem (pointed at the 1 O00 km altitude) is illustrated in Fig. 12. If a sensor is in orbit lower than 1 O00 km, a complementary relaxation of the pfd may be made. FIGURE 12 Discrimination of typical GSO ISS system from 1 O00 km (maximum pfd at 1 O00 km) O -5 - 10 - 15 - 20 - 25 - 30 - 35 - 40 1 O00
32、 900 800 700 600 500 400 300 200 100 O Altitude (km) 1339-12 Rec. ITU-R S.1339-1 3.6 A pfd threshold would limit the separation angle for some GSO ISS systems, as illustrated in Fig. 13. pfd impact on GSO ISS systems Separation limitation (degrees) to meet pfd limit of -147 dB(W/m2) in 100 MHz 15 14
33、6.5 FIGURE 13 View from the North Pole, ange to 1 O00 km , 1- 1 O00 km altitude O“: Angle required to meet pfd at 1 O00 km altitude 1339-13 Table 8 lists the maximum allowed orbital separation, as a function of theoretical design (line 1). Also computed is the operational limitation (line 5) from a
34、pfd of -128 and -147 dEi(W/m2) in 100 MHz, for the three systems which the theoretical design exceeds the pfd limit. This completes the analysis for case 1. TABLE 8 Maximum separation angle for GSO ISS systems Line 1 - W2A W2B w5 W6 162.6 78.6 53.9 111.1 162.6 Theoretical orbital separation (degrees
35、) 2 pfd at 1 O00 km (dB(W/m2) in 100 MHz) I -1022 -102.5 -172.2 -166.8 -150.6 -15.2 1,14:6 33.2 25.6 -170.8 -168.4 -105.2 46.8 44.8 -18.8 - - 159.3 - - 149.1 I 3 4 - -21.5 48.2 42.8 24.4 Separation limitation (degrees) to meet pfd 158.3 limit of -128 dB(W/m2) in 100 MHz 158.5 I 5 148.2 I Some GSO IS
36、S system may desire to operate with longitudinal separations of up to 162.6. However, when pfds of -128 to -147 dEi(W/m2) in 100 MHz are required, typical GSO ISS systems may be required to operate at smaller separations. 16 Rec. ITU-R S.1339-1 3.7 It was shown that a single entry pfd value of -147
37、dEi(W/m2) in 100 MHz will protect spaceborne passive sensors for all configurations of sensors and GSO ISS systems. A relaxation of this value (on the order of 10-20 dEi) may be achieved, depending on the characteristics of the specific systems studied. Conclusions with regard to analytic developmen
38、t of a pfd for GSO ISS 4 Conclusions In this Annex, methods were presented for calculating the interference into a low-Earth orbiting sensor satellite. These methods can be used to calculate the required criteria to meet the interference levels contained in Recommen- dation ITU-R SA.1029. A minimum
39、pfd level was developed that would protect all sensors from interference in all configurations. A pfd limit of -147 dEi(W/m2) in 100 MHz is sufficient to protect passive sensors from interference in all configurations of passive sensors and GSO ISS systems. For specific configurations of GSO ISS sys
40、tems and passive sensors, this value may be relaxed 10 to 20 dEi. It was also shown that sensors with calibration angles of between 75“ and 85“ from nadir will never take a calibration reading toward the GSO arc. Thus, a design objective of these sensors to utilize an 80“ calibration angle (as in th
41、e AMSU sensor) will enhance sharing with the GSO ISS. Analysis was presented on the interference of existing systems into proposed passive sensors. The analysis considered sensors operating in the EESS (passive), in an orbit with altitude less than 1000 km, and sun synchronous orbit inclination (close to 98.7“). In the Earth sensing mode, sensors are protected from emissions of GSO transmitters, via the sensor antenna back lobe. However, these sensors must take a “cold calibration reading“ toward deep space, and in this mode there is a possibility of interference from GSO transmitters.
