Introduction

Global warming is one of the most serious environmental problems for the planet Earth. The parameter known as SST is a useful indicator of global warming. It is very important to be able to monitor the SST continuously to clarify and to better understand the mechanism of global warming. Only spaceborne passive microwave radiometers in orbit on Earth exploration satellites can monitor the whole Earth SST on a continuing basis.

To observe the SST, the 4 200-4 400 MHz band is important from a scientific point of view. Since the EESS is allocated as secondary service in this band in RR No. 5.438 for passive sensing, it is desirable to upgrade the allocation to the primary status in the Table of Frequency Allocations to protect the future observations required in this band.

Aircraft radio altimeters which operate in the 4 200-4 400 MHz band are an integral part of aviation instrumentation. These instruments are widely utilized for determining the altitude of aircraft in flight and need to be protected from any possible interference due to the obvious safety of life aspects of their usage. Obviously, passive sensors cannot cause any interference into the radio altimeters since they do not emit any radio-frequency energy in the band. Possible interference from the radio altimeters into the passive sensors needs to be determined.

This Annex describes the potential for sharing the 4 200-4 400 MHz band with the existing primary allocated service, radio altimeters in the ARNS.