since the sun is in the same spot in each observation. A "frozen" orbit is the closest possible orbit to a circular orbit that is undisturbed by the oblateness of the Earth, gravitational attraction from the sun and moon, solar radiation pressure, and air drag. Mapping Terrain can be mapped from space with the use of satellites, such as Radarsat-1 and TerraSAR-X. International regulations According to the International Telecommunication Union (ITU), Earth exploration-satellite service (also: Earth exploration-satellite radiocommunication service) is – according to Article 1.51 of the ITU Radio Regulations (RR) – defined as: A radiocommunication service between earth stations and one or more space stations, which may include links between space stations, in which: information relating to the characteristics of the Earth and its natural phenomena, including data relating to the state of the environment, is obtained from passive or active sensors on satellites; similar information is collected from airborne or Earth-based platforms; such information may be distributed to earth stations within the system concerned; platform interrogation may be included. This service may also include feeder links necessary for its operation. Classification This radiocommunication service is classified in accordance with ITU Radio Regulations (article 1) as follows: Fixed service (article 1.20) Fixed-satellite service (article 1.21) Inter-satellite service (article 1.22) Earth exploration-satellite service Meteorological-satellite service (article 1.52) Frequency allocation The allocation of radio frequencies is provided according to Article 5 of the ITU Radio Regulations (edition 2012). In order to improve harmonisation in spectrum utilisation, the majority of service-allocations stipulated in this document were incorporated in national Tables of Frequency Allocations and Utilisations which is with-in the responsibility of the appropriate national administration. The allocation might be primary, secondary, exclusive, and shared. primary allocation: is indicated by writing in capital letters (see example below) secondary allocation: is indicated by small letters exclusive or shared utilization: is within the responsibility of administrations However, military usage, in bands where there is civil usage, will be in accordance with the ITU Radio Regulations. Example of frequency allocation See also Committee on Earth Observation Satellites Data collection satellite Earth observation Earth observation satellites transmission frequencies Earth Observing System - a NASA program comprising a series of satellite missions First images of Earth from space Imaging satellites List of Earth observation satellites Space telescope Satellite imagery GNSS radio occultation Microwave radiometer#Spaceborne Radar earth observation satellite Radar imaging Synthetic-aperture radar Interferometric synthetic-aperture radar Satellite altimetry References