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Agenda Item 1.6: 275 – 3000 GHz
Agenda Item 1.6, per Resolution 950 of WRC‐07, seeks to review Radio Regulations footnote No. 5.565
on passive use of spectrum between 275 and 1000 GHz in order to update the spectrum use by the
passive services and extend it to between 275 and 3000 GHz. In the current Table of Frequency
Allocations, bands above 275 GHz are not allocated. Radio Regulations footnote No. 5.565 makes
provisions for the use of these bands up to 1000 GHz for all services, including provisions meant to
protect passive services until, and if, such time as the table is extended. Protection of the bands 275‐
1000 GHz for passive use is considered to be highly desirable, with less emphasis on the 1‐3 THz regions.
Specific bands requiring protection are listed in Tables 1.6‐1 and 1.6‐3.
Recommendation: Administrations are urged to protect the bands given in Tables 1.6‐1 and 1.6‐3 from
harmful interference for use by the RAS and EESS, respectively.
RAS
Due to recent technological achievements, the exploration of the universe using the spectrum between
275‐3000 GHz has greatly expanded over the past decade. Extraordinary opportunities exist to study
the universe using this band, and include studies of the early universe, astrochemistry, planetary and
star formation, and supermassive black holes3. The current and future activities in the 275‐1000 GHz
regions are substantial, as evidenced by the work of instruments such as the James Clark Maxwell
Telescope (JCMT), the Caltech Submillimeter Observatory (CSO), the ARO’s Sub‐MM Telescope (SMT),
the Submillimeter Array (SMA) and the South Pole Telescope (SPT), and the on‐going construction of the
Atacama Large Mm/SubMm Array (ALMA). It is also contains regions that are currently used for passive
measurements, focused on the 1‐3 THz region, for NASA missions such as the Herschel Space
Observatory and the Stratospheric Observatory for Far‐Infrared Astronomy (SOFIA), and the future
space project Single Aperture Far‐Infrared Observatory (SAFIR). Because of high atmospheric
absorption due to water vapor above 1 THz, ground based observations can only be made from
extremely high sites, usually at elevations above 3km. Exploratory observations have been made in this
band, primarily around 1.5 THz. Because of the high horizontal opacity, interference from active
services located more than 10 km away is unlikely. In light of these developments it is worthwhile to
reexamine footnote 5.565 of the Table of Frequency Allocations.
The 275‐3000 GHz region, defined by the wavelength term “sub‐millimeter,” encompasses various
spectral windows that can be used for ground based astronomy. These are illustrated in Fig. 1.6.1 for the
frequency range 1‐1000 MHz. It is a prime region for spectroscopy and for studying continuum emission
from dust. In this frequency range, many of the common interstellar molecules such as CO, HCN, HCO+,
and CS have their higher energy rotational transitions (see table 1.6‐1).4 These spectral lines are
important probes of the interstellar medium where stars form, as they trace relatively hot (T > 200 K)
and dense (n > 107 cm‐3) gas. These transitions also trace circumstellar gas close to the stellar
photosphere, and can be used to elucidate the physical processes associated with evolved (i.e. giant)
3
National Research Council, Spectrum Management for Science in the 21st Century, The National Academies
Press, Washington, D.C., 2010.
4
The theory of quantum mechanics dictates that the rotational motion of molecules is characterized by discrete
energy levels. When a molecule changes energy levels, it makes a transition, and either emits or absorbs a photon
at a frequency proportional to the energy difference between the two levels.
9
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stars, including their mass loss and photospheric shocks. This region also contains the two fine structure
lines of neutral carbon (CI). The CI lines are used to study photon‐dominated regions, planetary nebulae,
and HII regions. This range furthermore has important significance for the investigation of
protoplanetary disks and their role in the origin of solar systems and life. In addition, the 275‐3000 GHz
region is the only spectral band containing the fundamental transitions of simple hydride species, such
as CH, OH, SiH, LiH, and SH. This is because the moments of inertia of these molecules are quite small,
resulting in large rotational energy splittings. Hydride molecules are extremely important for astronomy
for several reasons. First, the large energy difference between the rotational levels makes them efficient
coolants in dense gas. Also, because hydrogen is the most abundant element, hydride compounds are
common in diffuse and dense clouds. Moreover, hydride species are the basic building blocks of
interstellar chemistry. Understanding their abundances and distribution is key to chemical modeling. But
not all hydride species are known interstellar molecules primarily because their exact transition
frequencies have not been measured in many cases.
Future research in this largely unexplored spectral region is likely to yield additional spectral transitions
and continuum bands of interest to the passive services. Administrations are urged to protect the
passive services from harmful interference, particularly those bands to be used by ALMA (275‐375 GHz,
385‐500 GHz, 602‐720 GHz, and 787‐950 GHz).
The table below lists some important sub‐mm molecular tracers, their frequencies, and their use for
astronomy.
Table 1.6‐1 A Sample of Important Spectral Lines from 275 – 3000 GHz5
Spectral line Transition Frequency (GHz) Significance
CO 3‐2 345 Important tracer of galactic
4‐3 461 and extragalactic structure
5‐4 576 Probe of star‐forming regions
6‐5 691 and protoplanetary disks
7‐6 807
8‐7 922
etc6
CI Fine structure 492 Tracer of the ionized dense
809 interstellar medium, photon‐
dominated regions, planetary
nebulae
HCO+ 4‐3 356 Probe of high density
5‐4 446 regions, protostellar cores
6‐5 535
7‐6 624
HCN 4‐3 354 Probe of high density
5‐4 443 regions, protostellar cores,
5
To observe the listed transitions, fractional bandwidths of 1% are required for Galactic observations. Larger
bandwidths are needed for extragalactic measurements on the low‐frequency side because of the Doppler shift
caused by the recessional velocities of distant objects in the universe, e.g., a ten percent bandwidth is required to
cover the nearby clusters of galaxies of which our galaxy is a member.
6
Higher excitation lines occur throughout this band at intervals of 115.27 GHz, e.g. 922 GHz, 1037 GHz, etc.
Higher frequency transitions are excited by regions of increasingly high temperatures.
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6‐5 531 Inner shells of evolved stars
7‐6 620
8‐7 709
CS 7‐6 342 Dense protostellar cores,
8‐7 392 evolved stars, planetary
9‐8 440 nebulae
H2O 1(1,0)‐1(0,1) 556 Indicator of star formation,
2(1,1)‐2(0,2) 752 tracer for life, maser
1,1137
1(1,1)‐0(0,0) emission
H3O+ 0(0,0)‐1(0,1) 984 Important tracer of ion‐
1(1,0)‐1(1,1) 1,655 molecule chemistry
2(0,0)‐1(0,1) 2,972
H2D+ 1(1,0)‐1(1,1) 372 Probe of D/H isotope ratio,
3(2,1)‐3(2,2) 646 chemical fractionation
CH 1‐0 537 Important chemical building
2‐1 1,477 block, tracer of diffuse gas
OH 1‐0 2,560 Star formation, O‐rich
evolved stars.
Metal Hydrides 1‐0 Various Interstellar coolants
(SiH, LiH, MgH, 2‐1 Building blocks of interstellar
NaH, AlH) 3‐2 chemistry
Etc.
EESS
The Earth Exploration Satellite Service EESS(passive) currently uses spectrum in the range between 275
and 3000 GHz for several important measurements focusing on improving our understanding of the
atmosphere and providing information needed by policy makers. A list of a few of these uses is given in
Table 1.6‐2. Table 1.6‐3 gives a corresponding list of representative bands associated with these
measurements. The list is not exhaustive. As in the case of Radio Astronomy, these measurements
cannot be made in other bands because pressure‐broadened transitions of different atmospheric
constituents are being observed. In light of this and recent advances in relevant technologies, EESS use
of this portion of the spectrum is expected to increase significantly. It is therefore important that we
protect EESS use in this region of the spectrum.
Table 1.6‐2 Example EESS uses of spectrum from 275‐3000 GHz. This list highlights some significant
uses of the spectrum, but is not an exhaustive survey.
Use/Measurement/Target Significance
Mapping of ozone, polar 3D mapping of ozone in stratosphere to understand current
stratospheric clouds, chlorine ozone distribution and mechanisms for its depletion
sources
7
The atmosphere is highly opaque at these frequencies and protection would only be needed for measurements
above the atmosphere where satellite interference is possible.
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Cloud ice and frozen Key variable in the understanding of the water cycle, the
precipitation Earth’s energy budget, and the role of cloud feedback on the
climate—viewed in “window” regions around absorption
features from gaseous constituents
Upper troposphere and Key aspect of water cycle and important for determining
stratospheric water vapor climate feedback effects on radiative forcing in the presence
of increasing greenhouse gases—multiple bands are used
with varying sensitivity to water vapor, hence varying
applicability as a function of instrument scan type (nadir vs.
limb) and water vapor distribution
Stratospheric temperature 3D mapping of stratospheric temperature for understanding
atmospheric dynamics
Upper tropospheric pollution Understanding of distribution and transport of pollutants in
the upper troposphere
Trace gases 3D mapping of key atmospheric constituents (e.g., CO, SO2,
HCL, BrO, N2O) tied to carbon cycle, global climate,
pollution, atmospheric transport
Table 1.6‐3 Representative passive sensing bands and their associated measurements in 275‐1000
GHz.89
Total
Frequency bandwidth Measurement Existing or planned
Spectral line(s) (GHz)
(GHz) required instrument(s)
(MHz)
Window ( 276.4‐285.4)
276.33 (N2O),
275‐285.4 10 400
278.6 (ClO)
N2O, ClO, NO
Wing channel for
Window for 325.1, temperature sounding
298.5 (HNO3), 300.22
296‐306 10 000 (HOCl), 301.44 (N2O), Window (296‐306) MASTER
303.57 (O3), 305.2
(HNO3), 304.5 (O17O) N2O, O3 , O17O, HNO3,
HOCl
8
Adapted from: International Telecommunications Union, Working Party 7C, “Preliminary Draft New Report,
ITU‐R RS.[ABOVE 275] Passive bands of Interest to EESS/SRS from 275 to 3000 GHz: Annex 1313 to Working Party
7C Chairman’s Report,” September 30, 2009.
9
The atmosphere is highly opaque above 1000 GHz and protection would only be needed for measurements
where satellite interference is possible.
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Total
Frequency bandwidth Measurement Existing or planned
Spectral line(s) (GHz)
(GHz) required instrument(s)
(MHz)
{318.8, 345.8, 344.5}
(HNO3), 313.8 (HDO),
Water vapor sounding,
{321.15, 325.15} (H2O),
cloud ice, wing channel
{321, 345.5, 352.3,
for temperature
352.6, 352.8} (O3),
sounding
{322.8, 343.4} (HOCl), PREMIER, CIWSIR,
313.5‐355.6 42 100 345.8 (CO), {345.0, MASTER, MWI,
Window (339.5‐348.5)
345.4} (CH3Cl), 345.0 GOMAS, GEM
(O18O), 354.5 (HCN),
H2O, CH3Cl, HDO, ClO, O3
349.4 (CH3CN), {315.8,
, HNO3, HOCl, CO, O18O,
346.9, 344.5, 352.9}
HCN, CH3CN, N2O, BrO
(ClO), 351.67 (N2O),
346 (BrO)
Wing channel for water
vapor sounding
361‐365 4 000 364.32 (O3) GOMAS
O3
369.2‐391.2 22 000 380.2 (H2O) Water vapor sounding GEM, GOMAS
397‐399 2000 Water vapor sounding GOMAS
409‐411 2000 Temperature sounding
416‐433.46 17 460 424.7 (O2) Temperature sounding GEM, GOMAS
Water vapor profiling,
cloud ice
{443.1, 448} (H2O),
439.1‐466.3 27 200 MWI, CIWSIR
443.2 (O3), 442 (HNO3) Window (458.5‐466.3)
O3, HNO3, N2O, CO
477.75‐496.75 19 000 487.25 (O2) Temperature sounding Odin
Wing channel for water
vapor sounding
497.9 (N218O), {497.6, SOPRANO, MASTER,
497‐502 5000
497.9} (BrO), 498.6 (O3) Window (498‐502) Odin
O3, CH3Cl, N218O, BrO, ClO
523‐527 4 000 Window for 556.9 Wing channel for water
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Total
Frequency bandwidth Measurement Existing or planned
Spectral line(s) (GHz)
(GHz) required instrument(s)
(MHz)
vapor sounding
Window (523‐527)
{541.26, 542.35, Water vapor sounding
550.90, 556.98}
538‐581 43 000 (HNO3), 556.93 (H2O), Window (538‐542) Odin
{544.99, 566.29, 571.0}
(O3), 575.4 (ClO) HNO3, O3, ClO
620.7 (H2O), 624.27
(ClO2), {624.34, 624.89,
625.84, 626.17} (SO2),
{624.48, 624.78}
Water vapor sounding
(HNO3), 624.77 (81BrO),
624.8 (CH3CN), 625.04 MLS, SMILES,
ClO2, SO2, BrO, O3, H35Cl,
611.7‐629.7 18 000
(H2O2), 625.37 (O3), SOPRANO
CH3Cl, O18O, HOCl, HO2,
624.98 (H37Cl), 625.92
HNO3, CH3CN, H2O2
(H35Cl), 627.18 (CH3Cl),
627.77 (O18O), {625.07,
628.46} (HOCl), 625.66
(HO2)
Wing channel for water
635.87 (HOCl), 647.1
vapor sounding
(H218O), 649.45 (ClO),
649.24 (SO2), 649.7
Window (634.8‐651)
(HO2), 650.18 (81BrO),
634‐654 20 000 MLS, SMILES
650.28 (HNO3), 650.73 18
H2 O, HOCl, ClO, HO2,
(O3), 651.77 (NO),
BrO, HNO3, O3, NO, N2O,
652.83 (N2O)
SO2
Water vapor sounding,
658 (H2O), 660.49 cloud ice
(HO2), 688.5 (CH3Cl),
656.9‐692 35 100 CIWSIR, MWI, MLS
691.47 (CO), 687.7 Window (676.5‐689.5)
(ClO)
HO2, ClO, CO, CH3Cl
713.4‐717.4 4 000 715.4 (O2) O2
731 (HNO3), 731.18
O18O, HNO3
729‐733 4 000
(O18O)
750‐754 4 000 752 (H2O) Water vapor
771.8‐775.8 4 000 773.8 (O2) O2
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Total
Frequency bandwidth Measurement Existing or planned
Spectral line(s) (GHz)
(GHz) required instrument(s)
(MHz)
823.15‐845.15 22 000 834.15 (O2) O2
850‐854 4 000 852 (NO) NO
857.9‐861.9 4 000 859.9 (H2O) Water vapor
866‐882 16 000 Cloud ice CIWSIR
905.17‐927.17 22 000 916.17 (H2O) Water vapor
952 (NO), 955 (O18O) O18O, NO
951‐956 5 000 SOPRANO
968.31‐972.31 4 000 970.3 (H2O) Water vapor
985.9‐989.9 4 000 987.9 (H2O) Water vapor
15
