RVSM

[ursmunger]

Hallo,

 

habe nun eine Antwort von Eurocontrol erhalten betreffend Wetter-Korrekturen bei den HMU's.

 

Hier der Originaltext:

 

Dear Urs,

 

The HMU on line analysis programme deals with the Flight Level information

in the following way:

 

Automatically loaded into the HMU are the forecast altitudes of the Pressure

(Flight Levels). This of course is based upon the World Meteorological

Office Numerical Weather Prediction Model which uses as its input world wide

data from many sources including Radio Sonde, satellite data etc. The

forecast is for 6 hourly intervals and we interpolate to get a first level

cut at the expected altitude of the pressure level at any time.

 

EUROCONTROL Contributed to an ICAO Study carried out in the 1980s which

provided the data demonstrating that RVSM could be achieved. This ICAO Study

showed not only the nature of errors but also demonstrated that, averaged

over a large number of different aircraft the mean Altimetry System Error

tends to Zero. This study had local radio sonde data which enable this

conclusion to b obtained. We are using this feature in the HMU. The on line

program has a series of Kalman filters which look at the errors of the whole

set of aircraft passing the HMU in a given time window and identifies any

bias errors in this set of errors. This is used to correct the met data to

provide an improved height estimation. One risk associated with this method

is that should an aircraft be seen many times in a short period it can

adversely affect the data as it would bias the results according to that

aircraft's ASE. This is a rare event at the flight levels being studied but

has been observed at the original HMU at Strumble when there was a flight

test causing the aircraft to fly into and out of coverage. However the

Eurocontrol HMUs have a much larger area of coverage and in a much more

densely populated airspace and so the potential for a single aircraft to

bias the results is therefore much lower. However it is a potential event

that we have to be aware of.

 

 

In addition to the above on-line process, we also get from the met office

the data on actual Flight levels. These are needed for our GMU operation as,

unlike the HMU, the GMU cannot learn the met errors so we need the best data

available. This is passed to us up to 48 hours after the time to which it

applied. A manual action undertaken by our team in the Monitoring Cell is to

look at any aircraft showing a large Altimetry System Error, We look at the

aircraft's history to see if it is consistent with previous data from that

aircraft and also whether aircraft passing the HMU in the same period show

any problems. As part of that evaluation we look at both the forecast and

backcast data to observe the weather pattern. If there is a correlation

between the observed error and a rapidly changing weather pattern we discard

the measurement as we accept that the on-line methods used to estimate

Flight Level Altitude depend on stable conditions with only relatively

slowly varying pressure changes. By this method we have been able to

demonstrate monitoring accuracy meeting the ICAO requirements.

 

Roland Rawlings (RVSM Programme).

 

Ich hoffe, jetzt ist alles klar???

 

Gruss

Urs

[Hans Tobolla]

Hallo Urs,

 

vielen Dank für Deine Mühe. Die Antwort füllt genau die Lücke, die ich bei Messung des Anzeigefehler gesehen habe. Der Trick ist irgendwie genial, zumal auch noch viele andere wertvolle Daten dabei abfallen.

 

Ich gehe davon aus, dass die Beschreibung des Messverfahrens auch für die anderen Leser interessant ist.

 

Hast Du parat, was "GMU" bedeutet? Falls nicht, ist es auch kein Problem.

 

Viele Grüße!

 

Hans

[ursmunger]

Wenn ich's richtig im Kopf habe, heisst GMU 'GPS measuring unit'.

Dieses System berechnet auch den 'altimetry-error', aber soviel ich weiss, weniger genau.

 

Genaueres über die Funktionsweise findest Du auf

 

Gruss

Urs

 

 

[Dieser Beitrag wurde von ursmunger am 09. Februar 2002 editiert.]