1、 Recommendation ITU-R RS.1861(01/2010)Typical technical and operational characteristics of Earth exploration-satellite service (passive) systems using allocations between 1.4 and 275 GHzRS SeriesRemote sensing systemsii Rec. ITU-R RS.1861 Foreword The role of the Radiocommunication Sector is to ensu
2、re the rational, equitable, efficient and economical use of the radio-frequency spectrum by all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of
3、the Radiocommunication Sector are performed by World and Regional Radiocommunication Conferences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in
4、 Annex 1 of Resolution ITU-R 1. Forms to be used for the submission of patent statements and licensing declarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R pat
5、ent information database can also be found. Series of ITU-R Recommendations (Also available online at http:/www.itu.int/publ/R-REC/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (t
6、elevision) F Fixed service M Mobile, radiodetermination, amateur and related satellite services P Radiowave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed
7、 service systems SM Spectrum management SNG Satellite news gathering TF Time signals and frequency standards emissions V Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2010 ITU
8、 2010 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R RS.1861 1 RECOMMENDATION ITU-R RS.1861*Typical technical and operational characteristics of Earth exploration-satellite service (passive) systems using all
9、ocations between 1.4 and 275 GHz (Question ITU-R 243/7) (2010) Scope This Recommendation provides typical technical and operational characteristics of Earth exploration-satellite service (passive) systems using allocations between 1.4 and 275 GHz for utilization in sharing studies. The ITU Radiocomm
10、unication Assembly, considering a) that Earth exploration-satellite service (EESS) (passive) observations may receive emissions from active services; b) that there are exclusive EESS (passive) allocations in which all emissions are prohibited by RR No. 5.340; c) that EESS (passive) is allocated on a
11、 co-primary basis with active services in certain bands; d) that studies considering protection for EESS (passive) systems are taking place within ITU-R; e) that in order to perform compatibility and sharing studies with EESS (passive) systems, the technical and operational characteristics of those
12、systems must be known, recommends 1 that the technical and operational parameters presented in Annex 1 of this Recommendation should be taken into account in studies considering EESS (passive) systems using allocations between 1.4 and 275 GHz. Annex 1 1 Introduction Passive sensors are used in the r
13、emote sensing of the Earth and its atmosphere by Earth exploration and meteorological satellites in certain frequency bands allocated to the Earth exploration-satellite service (EESS) (passive). The products of these passive sensor operations are used extensively in meteorology, climatology, and oth
14、er disciplines for operational and scientific purposes. However, these sensors are sensitive to any emissions within their allocated band. Therefore, any RF emissions above a certain level may constitute interference to the passive sensors using those bands. *This Recommendation should be brought to
15、 the attention of Radiocommunication Study Group 1. 2 Rec. ITU-R RS.1861 This is mainly due to the fact that passive sensors may not be able to differentiate the wanted signal from the interference and that interference may not be identifiable in the passive sensor products. 2 Current missions and p
16、redicted deployments Several administrations and at least one recognized international organization operated more than 24 satellites in the EESS (passive) at the end of the year 2007. An additional two to three are anticipated to be deployed per year for the foreseeable future. Individual satellites
17、 typically carry one to three passive sensing payloads operating below 275 GHz. Each payload may conduct measurements simultaneously at 3 to 15 frequencies as well as on two polarizations at a single frequency. 3 Typical orbits EESS (passive) systems operate in non-geostationary satellite orbit (non
18、-GSO). Orbits are typically circular with an altitude between 350 and 1 400 km. Many EESS (passive) systems operate in a sun-synchronous orbit. Some sensors make measurements at the same place on the Earth every day, while others will repeat observations only after a longer (often more than two week
19、s) repeat period. In certain circumstances, multiple satellites operate in formation. Formation flying EESS satellites allow the capability to measure a portion of the atmosphere or surface of the Earth using both multiple instruments and multiple orientations. Measurements from multiple spacecraft
20、will be separated within an amount of time shorter than the time constant of the phenomena being measured. Nominally this separation is on the order of 5 to 15 min, but can be as little as 15 s. Two formations are used between multiple systems operating in non-GSO. In one formation, two or more sate
21、llites directly follow each other performing measurements of the same parcel of atmosphere or the Earths surface as demonstrated by satellites A and B in Fig. 1. In the other formation, a nadir pointing passive sensor conducts a measurement while another spacecraft conducts a near-simultaneous measu
22、rement at the Earths limb as demonstrated by satellites A and C in Fig. 1. 4 Types of measurements All EESS passive sensing systems perform a form of radiometry. Radiometry senses how much energy a body radiates given its temperature. The amount of energy radiated from a perfect “blackbody” varies w
23、ith frequency and is given by Plancks equation. However, no substance is truly a perfect blackbody radiator. Frequencies of particular interest for EESS (passive) applications are provided in Recommendation ITU-R RS.515. The amount of energy radiated is also dependent on the radiating substance. Wit
24、hin a passive sensors field of view, there may be multiple radiators in inter alia atmosphere, water vapour, suspended ice particles, and cloud liquid water, emitting in the sensors bandwidth. Measurements not conducted on the Earths limb will also receive background emissions from water, soil, surf
25、ace ice, or some combination of all three. A single passive sensor cannot by itself identify how much energy is radiated by each substance in its field of view. For this reason, data products of most value are derived by comparing measurements from multiple sensors operating at multiple frequencies.
26、 By performing radiometric measurements at multiple frequencies, the types of each natural emitter (e.g. water vapour, suspended ice, O3, etc.) and their concentrations may be derived. As the data from any one sensor Rec. ITU-R RS.1861 3 may be compared with that of multiple other sensors, any inter
27、ference received by one sensor may corrupt multiple other measurements. FIGURE 1 Formation flying orientations 1861-01BNon-GSOAtmosphereAC4.1 Fixed-pointing, multiple frequency and polarization radiometric sensing Sensing concurrently at multiple frequencies and polarizations offers the possibilitie
28、s of identifying the presence of multiple natural emitters present in the field of view of the sensor as well as to create profiles of their concentrations. Profiling (a.k.a. sounding) sensors may be nadir-pointing or pointed at the limb of the Earth. Applications of profiling sensors includes the d
29、etermination of atmospheric chemistry profiles of H2O, O3, ClO, BrO, HCl, OH, HO2, HNO3, HCN, and N2O through limb measurements. Fixed pointing radiometers are also used to determine path delay of the radar signals used for altimeters caused by atmospheric water vapour. Radiometers designed for the
30、whole Earth viewing perform continuous, hemispheric microwave soundings of temperature and humidity profiles as well as rain mapping. 4.2 Conical scanning radiometers Many passive microwave sensors designed for imaging the Earths surface features use a conical scan configuration turning around the n
31、adir direction because it is important, for the interpretation of surface measurements, to maintain a constant ground incidence angle along the entire scan-lines since the footprints will remain constant in size, and also because the polarization characteristics of the signal have an angular depende
32、nce. Conical scanning antennas gather information over wide areas as shown in Fig. 2. Scans are typically performed by rotating the antenna at an offset angle from the nadir direction. Conical scanning radiometers are used to monitor various water processes including precipitation, oceanic water vap
33、our, cloud water, near-surface wind speed, sea surface temperature, soil moisture, snow cover, and sea ice parameters. They can also be used to provide information on the integrated column precipitation content, its area distribution, and its intensity. 4 Rec. ITU-R RS.1861 FIGURE 2 Geometry of coni
34、cal scan passive microwave radiometers 1861-02Useful scan-angleUsefulswathIFOVConical scanaroundnadir directionIncidenceangleSatellite subtrackPixelGeometry of conically scanned microwave4.3 Cross-track scanning radiometers Scanning radiometric measurements gather information over wide areas creatin
35、g virtual maps of the parameter being measured. This data product determines the horizontal spatial variability of a parameter rather than measuring the parameters at specific points. Scanning measurements are also typically performed at multiple frequencies and polarizations. Typical applications o
36、f cross-track scanning radiometers include the measurement of temperature profiles in the upper atmosphere (especially the stratosphere) and to provide a cloud-filtering capability for tropospheric temperature observations. They also are used to provide daily global observations of temperature and m
37、oisture profiles at high temporal resolution, and to measure cloud liquid water content and provide qualitative estimates of precipitation rate. Scans are typically performed in a cross-track pattern across the surface of the Earth as shown in Fig. 3. Cross-track scanning is performed by physically
38、rotating a reflector 360. As the reflector is directed away from the surface of the Earth, sensor channels are still used as calibrations are performed by measuring the cosmic background (i.e. cold sky) in addition to a known “warm” source on the spacecraft, as shown in Fig. 4. Rec. ITU-R RS.1861 5
39、FIGURE 3 Typical cross-track Earth scanning pattern 1861-03MotorDirection ofrotationReflectorDetectorInstantaneousfield of view(IFOV)ScandirectionField ofview (FOV)Directionof travelGroundresolutionFIGURE 4 Typical sensing scanning pattern over 360 1861-04Direction ofrrotationeflector295 Sensing cha
40、nnelson for Earth sensingNadir65 Sensingchannels off199.4 Sensing channels on for warm calibration205 Warm load position210.6 Sensing channels off145.6 Sensing channels off140 Cold sky position134.4 Sensing channelson for cold calibrationNote 1 All angles with respect to nadir.4.4 Push-broom radiome
41、ters A “push-broom” (along track) sensor consists of a line of sensors arranged perpendicular to the flight direction of the spacecraft, as illustrated in Fig. 5. Different areas of the surface are detected as the spacecraft flies forward. The push-broom is a purely static instrument with no moving
42、parts. 6 Rec. ITU-R RS.1861 The major feature of the push-broom is that all resolution elements in a scan line are acquired simultaneously, and not sequentially as with mechanically scanned sensors, enabling this type of sensor to significantly increase the achievable radiometric resolution. Push-br
43、oom sensors can be used for a variety of applications, including temperature profiles measurements of the atmosphere, and soil moisture and ocean salinity measurements. FIGURE 5 Typical push-broom radiometer configuration 1861-055 Definition of parameters TABLE 1 List of technical and operational EE
44、SS parameters for passive sensors Sensor type Orbit parameters Altitude Inclination Eccentricity Repeat period Sensor antenna parameters Number of beams Reflector diameter Maximum antenna gain Polarization 3 dB beamwidth Instantaneous field of view Off-nadir pointing angle Incidence angle at Earth R
45、ec. ITU-R RS.1861 7 TABLE 1 (end) 3 dB beam dimensions Swath width Main beam efficiency Beam dynamics Sensor antenna pattern Cold calibration antenna gain Cold calibration horizontal angle (degrees relative to satellite track) Cold calibration vertical angle (degrees relative to nadir direction) Sen
46、sor receiver parameters Sensor integration time Channel bandwidth Horizontal resolution Vertical resolution TABLE 2 Definitions of parameters Parameter Definition Sensor type Various types of radiometers are possible depending on the technology of the radiometer: interferometric radiometer, conical
47、scan, nadir, push-broom, limb radiometer Orbit parameters Altitude The height above the mean sea level Inclination Angle between the equator and the plane of the orbit Eccentricity The ratio of the distance between the foci of the (elliptical) orbit to the length of the major axis Repeat period The
48、time for the footprint of the antenna beam to return to (approximately) the same geographic location Sensor antenna parameters Antenna characteristics vary among sensors. Measured antenna patterns are provided in 6, where available. A reference radiation pattern is currently being developed for use
49、in other cases Number of beams The number of beams is the number of locations on Earth from which data are acquired at one time Reflector diameter Diameter of the antenna reflector Maximum antenna gain The maximum antenna gain can be the real one, or, if it is not known, it can be computed using the antenna efficiency and D diameter of the reflector (when applicable), with the formula: 2tenna_gainMaximum_an =DPolarization Specification of linear or circular polarization 3 dB beamwidth The 3 dB beamwidth, 3dB, is defined as the angle between the two dire
