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Distance Measuring Equipment (DME)
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According to NTIA:
DME and TACAN are very similar in their functional performance. DME systems operate between the bands 962-1213 MHz and are usually co-located with a very high frequency (VHF) Omni-directional Range (VOR) operating in the band 108-118 MHz to provide the distance and azimuth from the aircraft to the DME transmitter. An important requirement is a frequency separation of 63 MHz between the interrogation and the reply frequency. This accommodates the pulse-pair shaping and signal processing bandwidth necessary to achieve individual system integrity. This procedure leaves only 126 possible frequency pairs throughout the band 962-1213 MHz. DME and VOR operate in paired channels so at any given location, both the VOR and DME proposed assignments must “pass” their channel planning criteria. This puts additional constraints on DME assignments.
DME allows aircraft to fly safe, accurate paths during the en-route, terminal, landing, missed approach and departure phases of flight. The system provides aircraft pilots with the slant range to a ground-based transponder station. The ground-based transponder system is air-initiated, with the airborne transmitter interrogating a transponder, and calculating range from the time difference between the initiation of the interrogation and receipt of the reply. The maximum range for high altitude service (18km) is 240 km and for low altitude, service (5.5 km) the distance is 74 km. The maximum range for the standard terminal service is 46 km for an altitude of 3.7 km.
TACAN is a tactical air navigation system for the military services used ashore, afloat, and airborne. TACAN is primarily collocated with the civil VOR stations (VORTAC facilities) to enable military aircraft to operate in the NAS and to provide DME information to civil users. The Navy, Coast Guard, and Military Sealift Command (MSC) operate several hundred sea-based TACAN stations.
The FAA operates approximately 60 VOR, 405 VOR/DME, and 590 VORTAC ground stations, as well as another 30 DMEs. Other Federal agencies, state and local governments, and private entities also own some of these facilities.
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Frequency Bands |
| Band | Use | Service | Table |
| 960 - 1215 MHz | Distance Measuring Equipment (DME) | Aeronautical Radionavigation | F |
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Soil Moisture Active Passive (SMAP) Satellite
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The Soil Moisture Active Passive (SMAP) satellite is a planned NASA satellite mission to monitor soil moisture around the globe. It is planned for launch in 2014.
As its name implies, the Soil Moisture Active Passive (SMAP) satellite uses active and passive radio systems to measure soil moisture around the globe. The spacecraft is in a sun-syncronous orbit that passes overhead of its target areas around 6 AM and 6 PM, approximately every 3 days at the equator and every 2 days at high latitudes.
SMAP's sensors can determine soil moisture down to a depth of approximately 5-10 cm. The active radar provides approximately 3 km resolution on the ground, using a 6 m antenna and measuring reflections in HH, VV, and HV polarization modes. The radar works in frequency hopping mode to avoid interference to and from aviation radars that operate in the same band. The instantaneous signal from the radar consists of two separate signals each of ~1.4 MHz bandwidth, separated by 5 MHz. It pulses every ~354 microseconds, for a duration of ~10-20 microseconds per pulse. The radar transmit power (not EIRP) is a few hundred watts.
SMAP will operate in a circular orbit of 670 km altitude. The ground footprint of the radar is approximately 1000 km. Resolution of the radar in low-resolution mode is approximately 40 km, and in high-resolution mode the resolution is approximately 3 km.
Soil moisture data can be used for improving numerical weather prediction, including seasonal climate prediction and rainfall prediction.
Like the European SMOS satellite, it is anticipated that SMAP's passive sensor will be subject to illegal RFI in the passive-only 1400-1427 MHz band.
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Frequency Bands |
| Band | Use | Service | Table |
| 1200 - 1300 MHz | SMAP active radar | Earth Exploration-satellite | F |
| 1400 - 1427 MHz | SMAP passive radiometer | Earth Exploration-satellite | F |
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