doc.: IEEE /0013r0 Submission April 2008 Joel Johnson, IEEE GRSSSlide 1 Coexistence Issues for Passive Earth Sensing from GHz Notice: This document has been prepared to assist IEEE It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Date: Authors:

doc.: IEEE /0013r0 Submission April 2008 Joel Johnson, IEEE GRSSSlide 2 Abstract Important meteorological observations are conducted in the GHz band by passive microwave systems on Earth observing satellites. The Earth Observing Satellite Service (EESS) has a shared primary international frequency allocation from GHz, other frequencies have been used opportunistically Apparently no detailed co-existence analyses have been performed for currently proposed or standards. Here an initial co-existence analysis is provided to show that co- existence may be an issue and more detailed analyses should be performed

doc.: IEEE /0013r0 Submission April 2008 Joel Johnson, IEEE GRSSSlide 3 Passive Microwave Observations Passive microwave systems (microwave radiometers) have a long history of providing vital meteorological measurements Systems are receive-only, and observe naturally emitted thermal noise from the Earth’s environment Frequencies near the 60 GHz oxygen absorption line are critical for obtaining atmospheric temperature profiles; this is done by using several radiometer frequencies at varying locations along the line Current and future US and international satellites are using these frequencies, including the AMSU and SSMI/S sensors on-board several defense meteorological satellites ITU regulations recognize the importance of these frequencies for the Earth observations by providing the EESS (passive) service with a shared primary allocation from GHz

doc.: IEEE /0013r0 Submission April 2008 Joel Johnson, IEEE GRSSSlide 4 ITU Frequency Allocations GHz EARTH EXPLORATION-SATELLITE (passive) FIXED INTER-SATELLITE MOBILE SPACE RESEARCH (passive) A A EARTH EXPLORATION-SATELLITE (passive) FIXED MOBILE SPACE RESEARCH (passive) EARTH EXPLORATION-SATELLITE (passive) FIXED INTER-SATELLITE MOBILE RADIOLOCATION SPACE RESEARCH (passive) 5.556A A FIXED INTER-SATELLITE MOBILE RADIOLOCATION ▲ ▲

doc.: IEEE /0013r0 Submission April 2008 Joel Johnson, IEEE GRSSSlide 5 ITU Footnotes (None for EESS) The bands GHz, GHz, GHz, GHz, GHz and GHz are available for high-density applications in the fixed service (see Resolutions 75 (WRC-2000) and 79 (WRC-2000)). Administrations should take this into account when considering regulatory provisions in relation to these bands. Because of the potential deployment of high-density applications in the fixed-satellite service in the bands GHz and GHz (see No B), administrations should further take into account potential constraints to high-density applications in the fixed service, as appropriate. (WRC-03) In the bands GHz, GHz and GHz, radio astronomy observations may be carried out under national arrangements. (WRC-2000) 5.556A Use of the bands GHz, GHz and GHz by the inter-satellite service is limited to satellites in the geostationary-satellite orbit. The single-entry power flux- density at all altitudes from 0 km to km above the Earth's surface produced by a station in the inter-satellite service, for all conditions and for all methods of modulation, shall not exceed -147 dB(W/(m² × 100 MHz)) for all angles of arrival. (WRC-97) Additional allocation: in Japan, the band GHz is also allocated to the radiolocation service on a primary basis. (WRC-97) In the bands GHz, GHz, GHz, GHz, GHz, GHz and GHz, stations in the aeronautical mobile service may be operated subject to not causing harmful interference to the inter-satellite service (see No. 5.43) In the band GHz, airborne radars in the radiolocation service may be operated subject to not causing harmful interference to the inter-satellite service (see No. 5.43).

doc.: IEEE /0013r0 Submission April 2008 Joel Johnson, IEEE GRSSSlide 6 ITU RS ITU recommendation RS also addresses the EESS service from GHz –Sets a received power limit of -169 dBw not to be exceeded either 0.01% of the time or area –this is 0.01K in a 100 MHz radiometer bandwidth

doc.: IEEE /0013r0 Submission April 2008 Joel Johnson, IEEE GRSSSlide 7 Initial Co-Existence Analysis Radiometer is just a receiver with given antenna properties –Concern is the impact on the observed noise power –Convert non-thermal received powers into an increase in observed antenna temperature given radiometer channel bandwidth Use Friis formula as starting point for received power Pr: Requires knowledge of: – transmitted power (Pt) –antenna gain of transmitter in direction of radiometer (Gt) –radiometer antenna effective area (Aeff) in direction of transmitter –Range to radiometer (R) –atmospheric attenuation (exp(-tau))

doc.: IEEE /0013r0 Submission April 2008 Joel Johnson, IEEE GRSSSlide 8 Co-Existence Analysis (2) EIRP (PtGt) assumed to add for N sources within radiometer antenna footprint –Some sort of antenna pattern averaging would be included in this –Transmit antenna pattern issues not clear at present –Also need to account for any scattering effects into radiometer beam Relating the radiometer effective aperture to gain, then beamwidth, we get (assuming transmitter in radiometer main beam) where A is the radiometer footprint area on the ground Now relate this to a change in brightness temperature through where B=radiometer bandwidth and k=Boltzmann’s const

doc.: IEEE /0013r0 Submission April 2008 Joel Johnson, IEEE GRSSSlide 9 Co-Existence Analysis (3) This gives the EIRP/(footprint area) (a “density of interferers”) to produce a given change in temperature: Using the 57 GHz wavelength and simplifying gives where TdB is the atmospheric attenuation (positive dB) We can use this equation to examine interference for current and future spaceborne radiometers

doc.: IEEE /0013r0 Submission April 2008 Joel Johnson, IEEE GRSSSlide 10 What are reasonable numbers in this equation? An antenna temperature perturbation of 0.01 to K is justifiable –ITU RS uses 0.01K in 100 MHz –Such small changes are important for climate studies –Current systems can achieve these accuracies when averaged over time or space Spot area: Footprint area of 2000 square kilometers assumed (AMSU instrument) Bandwidth: Use the 100 MHz specified in RS

doc.: IEEE /0013r0 Submission April 2008 Joel Johnson, IEEE GRSSSlide 11 Zenith Atmospheric Attenuation Compute using ITU P676-7 algorithms:

doc.: IEEE /0013r0 Submission April 2008 Joel Johnson, IEEE GRSSSlide 12 Comments on Zenith Attenuation For sea level transmitters, minimum is around GHz (even lower at 64 GHz) Transmitters at higher elevations (e.g. Denver) have minimum around 80 dB No accounting here for through wall attenuation etc. Is there any possibility of transmitters at higher altitudes (i.e. airborne?) Results also depend weakly on atmospheric conditions, ITU separates into different climate regions

doc.: IEEE /0013r0 Submission April 2008 Joel Johnson, IEEE GRSSSlide 13 Final result Putting this all together (80 dB attenuation) yields or in Watts Can also be re-written as where N’ is the number of transmitters per square km EIRP needs to include the fact that the radiometer main beam is likely in a sidelobe of the transmit antenna, as well as any scattering issues

doc.: IEEE /0013r0 Submission April 2008 Joel Johnson, IEEE GRSSSlide 14 Conclusion Preliminary analysis performed here suggests that there is a potential for future GHz systems to impact passive EESS service However analysis presented here needs refinement –Improve antenna, scattering, and ground propagation analysis –Expected density of transmitters an issue Suggest that more careful analysis should be performed –Should problem be shown to be definite, next steps need to be considered –More information at: