Transcript Presentation - Copernicus.org

Forecasting
Runway Visual Range
ECAM
Lauren Reid, Met Office, 12 September 2013
© Crown copyright Met Office
Contents
This presentation covers the following areas
• Introduction
• Definition of RVR
• Methodology
• Models (UKV, MONIM, HT-FRTC)
• Case studies
• Conclusions
• Questions and answers
© Crown copyright Met Office
Introduction
• Runway Visual Range (RVR) is used at airports
to help determine if Low Visibility Procedures
(LVP) are necessary.
• LVPs affect airport operations by requiring a
reduction in the number of aircraft landing and
taking-off depending on the cloud base height,
visibility and/or RVR
• The purpose of this study was to determine if it
may be possible to generate an RVR forecast to
aid airport operations mitigating against the
worst impacts of LVP
© Crown copyright Met Office
RVR ≠ Visibility
The view from the cockpit along runway 22R at
Copenhagen during a fog event. The RVR in this photo is 500m [1]
© Crown copyright Met Office
[1]
http://picsfromtheoffice.blogspot.co.uk/2011_11_01_archive.html - Mathieu Neuforge
Definitions
Runway Visual Range is defined by ICAO Annex 3 as:
The range over which the pilot of an aircraft on the centre line of a
runway can see the runway surface markings or the lights
delineating the runway or identifying its centre line.
Visibility - Visibility for aeronautical purposes is the greater of:
a) the greatest distance at which a black object of suitable
dimensions, situated near the ground, can be seen and
recognized when observed against a bright background;
b) the greatest distance at which lights in the vicinity of 1 000
candelas can be seen and identified against an unlit background.
Note — The two distances have different values in air of a given
extinction coefficient, and the latter b) varies with the
background illumination. The former a) is represented by the
meteorological optical range (MOR). (ICAO Document 9328
2005):
© Crown copyright Met Office
Relationships
• Koschmieder's Law. A relationship between
the apparent luminance contrast of an object,
seen against the horizon sky by a distant
observer, where σ = extinction coefficient (m-1)
MOR 
 ln(0.05)

• Allard's Law. An equation relating illuminance
(E) produced by a point source of light of
intensity (I) on a plane normal to the line of
sight, at distance (R) from the source, in an
atmosphere having a transmissivity (T).
E=(Ie-σR)/R2
© Crown copyright Met Office
• The equations from
Koschmieder and
Allard’s Law can be
rearranged to form:
MOR 
 ln(0.05) RVRLL
ln( I )  2 ln( RVRLL )
Et
© Crown copyright Met Office
An illustration of the variation of RVR with MOR for a fixed
illumination threshold (Et=10-5) derived from the equation on
previous page. Results are displayed for a range of runway lighting
intensity (I) from 10 cd to 10000 cd (shown as different colours).
Data
© Crown copyright Met Office
MONIM
(Met Office Might Illumination Model)
• MONIM is used by defence as a tactical decision aide for use with
night vision goggles.
• Adapted for use in built up areas with additional light sources.
• Results in the illumination value, E.
• Et is required for the RVR calculation, so the ratio of the background
light vs the whole hemisphere is utilised - 0.137%
© Crown copyright Met Office
HT-FRTC
(Havemann-Taylor Fast Radiative
Transfer Code)
• The Havemann-Taylor Fast Radiative Transfer
Code was developed at the Met Office for use
in simulating the electromagnetic radiation from
a source at a specified observation location
some distance away
• As the electromagnetic radiation travels to the
observer, the radiation is modified by the
atmosphere, which absorbs, emits and scatters
the radiation by varying amounts depending on
the current state of the atmosphere
© Crown copyright Met Office
Met Office UKV model
Output fields from the UKV model valid at
06z 16 October 2011. Left: Visibility at 1.5m
height (m). Right: Fog fraction (percentage).
© Crown copyright Met Office
• The ability to accurately
forecast fog and the
subsequent low visibility
is incredibly important
for airport operations, it
is important to recognise
that fog is one of the
most difficult
meteorological
phenomena to forecast
with the level of detail
required.
Observations
Transmissometer
• The three transmissometers record and store the
details of the runway lighting, including the
background luminance (cd/m2) and the runway light
intensity (cd). If the observed RVR is above 1500m
then the system does not record the RVR
METAR (Meteorological Terminal Air Report)
• Is a routine meteorological observation given at all
airports. METARs give an indication to incoming pilots
of the current weather conditions at the runway and
includes: temperature; pressure; cloud height and
coverage (in octa); wind speed and direction; visibility;
and RVR (if below 1500m).
These two methods used to identify and test case
studies at Heathrow and Bournemouth
© Crown copyright Met Office
Heathrow AP 16-10-2011
METAR and IRVR Obsevations at Touchdown Point
2000
1800
RVR Touch
down South
1600
Distance (m)
1400
RVR Touch
down North
1200
1000
METAR RVR
North
800
600
400
METAR RVR
South
200
0
02:00
04:00
06:00
08:00
10:00
Time of day
Examples of the output
transmissometer RVR for Heathrow
Airport on 16 October 2011.
a) Shows only the first (touch down)
value of RVR from the
transmissometer. Note how the METAR
values for both the northern and
southern runway match with the IRVR
data.
Heathrow AP 16-10-2011
METAR and Average IRVR Obsevations
2000
calc MOR
1800
1600
avg I-RVR South
Distance (m)
1400
avg I-RVR North
1200
1000
METAR RVR
North
800
600
METAR RVR
South
400
METAR VIS
200
0
02:00
04:00
© Crown copyright Met Office
06:00
Time of day
08:00
10:00
b) There are three reported values for
the RVR for the north and south
runways which has been averaged to
give the blue and red line, from this the
MOR for the northern runway was
calculated (green). The overlaid points
are the METAR RVR (for both runways)
and visibility in blue, red and green
respectively.
Case Studies
© Crown copyright Met Office
Case Studies
• Dates were chosen for the case studies based
on METAR observations of RVR that lasted
longer than 3.5 hours and resulted in a
significant reduction in visibility at Heathrow or
Bournemouth Airports.
• The dates investigated were:
• 30th September 2011 at Bournemouth
• 16th October 2011 at Heathrow
• 20th September 2011 at both sites
© Crown copyright Met Office
Bournemouth Airport
30 September 2011
4000
Bournemouth AP 30-09-2011 (METAR and IRVR Obsevations)
3500
calc MOR
3000
Distance (m)
avg I-RVR
2500
METAR
VIS
2000
1500
METAR
RVR R26
1000
METAR
RVR R08
500
0
02:00
03:00
04:00
05:00
06:00
Tim e of day
© Crown copyright Met Office
07:00
08:00
Bournemouth Airport
30 September 2011
Forecast Time
UKV Visibility
(m)
36km box
Average (m)
Percentage Fog
(0-1)
METAR Visibility
(m)
METAR RVR (m)
03z (T+0)
4508
6046
0.125
1000
R26/0450
R08/0600
04z (T+1)
4668
5488
0.125
900
R26/P1500
R08/0250
05z (T+2)
5408
5953
0.00
200
R26/0250
R08/0300
06z (T+3)
5754
6293
0.00
100
R26/0400
07z (T+4)
6376
6685
0.00
600
R26/0175
08z (T+5)
7783
8858
0.00
4000
-
09z (T+6)
11083
11731
0.00
9000
-
10z (T+7)
12254
13414
0.00
CAVOK
-
11z (T+8)
12379
13365
0.00
CAVOK
-
© Crown copyright Met Office
HT-FRTC: Obs of visibility and forecast RVR
Bournemouth 20110930
6000
METAR RVR
R26
Distance (m)
5000
4000
METAR RVR
R08
3000
Continental,
I=3000
2000
Koschmieder MOR
1000
0
03:00
04:00
05:00
06:00
07:00
08:00
09:00
Time
The minimum and maximum
differences plus RMSE in metres
of RVR using the forecast NWP
input compared to the average
transmissometer observations.
© Crown copyright Met Office
Difference
RVR (m)
Minimum
2338
Maximum
4303
RMSE
3514
Bournemouth Airport
30 September 2011
• Poor visibility forecast unrepresentative of the
conditions experienced
• The other case study also had a similar
situation where the forecast visibility was too
large resulting in unrealistic RVR forecast
• As Bournemouth has a costal location this
impacts on fog formation in the region
© Crown copyright Met Office
Heathrow Airport
16 October 2011
Heathrow AP 16-10-2011
METAR and Average IRVR Obsevations
2000
calc MOR
1800
1600
avg I-RVR South
Distance (m)
1400
avg I-RVR North
1200
1000
METAR RVR
North
800
600
METAR RVR
South
400
METAR VIS
200
0
02:00
04:00
06:00
Time of day
© Crown copyright Met Office
08:00
10:00
Heathrow Airport
16 October 2011
© Crown copyright Met Office
Heathrow Airport
16 October 2011 - sensitivity
Sensitivity study: Obs of visibility and forecast RVR
Heathrow 20111016
2000
METAR
RVR R27L
1800
Distance (m)
1600
METAR
RVR R27R
1400
1200
IRVR data
1000
800
MONIM Et,
I=3000
600
400
IRVR avg
200
0
03:00
04:00
05:00
06:00
07:00
Time
© Crown copyright Met Office
08:00
09:00
10:00
HT-FRTC: Obs of visibility and forecast RVR
Heathrow 20111016
3500
METAR RVR
R27L
Distance (m)
3000
2500
METAR RVR
R27R
2000
1500
Continental,
I=3000
1000
500
Koschmieder MOR
0
03:00
04:00
05:00
06:00
07:00
08:00
09:00
10:00
Time
The minimum and maximum
differences plus RMSE of the RVR
using the forecast NWP input
compared to the average
transmissometer observations.
© Crown copyright Met Office
Difference
RVR (m)
Minimum
-141
Maximum
2691
RMSE
1722
Heathrow Airport
16 October 2011
• Fog/visibility forecast was reflective of the
observed conditions
• The forecast data used in the RVR forecast did
result in a good approximation of the RVR
though it did tend to be too large compared to
the METARs
© Crown copyright Met Office
Conclusions
• When using obviations as inputs to the RVR
calculation RMS error is in the region of 300900m.
• When using the forecast visibility the RVR can
degrade significantly to be over 2000m larger
than the observations.
• It is possible to forecast RVR, but only if the
forecast visibility and low level cloud is an
accurate representation of the conditions
experienced
© Crown copyright Met Office
Questions & answers
© Crown copyright Met Office
RVR Definition
• Runway visual range is defined by ICAO Annex 3 as:
The range over which the pilot of an aircraft on the centre
line of a runway can see the runway surface markings or
the lights delineating the runway or identifying its centre
line.
• Further details are given by ICAO Doc 9328 section 2.2:
The definition implies that RVR is not an “observation” or a
“measurement” of a meteorological parameter such as
surface wind direction and speed, temperature and
pressure; it is an assessment, based on calculations that
take into account various elements, including
atmospheric factors such as extinction coefficient of the
atmosphere, physical/biological factors such as visual
threshold of illumination, and operational factors such as
runway light intensity.
© Crown copyright Met Office
Visibility Definitions
The definitions of visibility and meteorological optical range are
(ICAO Document 9328 2005):
Visibility - Visibility for aeronautical purposes is the greater of:
a) the greatest distance at which a black object of suitable
dimensions, situated near the ground, can be seen and
recognized when observed against a bright background;
b) the greatest distance at which lights in the vicinity of 1 000
candelas can be seen and identified against an unlit background.
Note — The two distances have different values in air of a given
extinction coefficient, and the latter b) varies with the
background illumination. The former a) is represented by the
meteorological optical range (MOR).
Meteorological Optical Range (MOR) - The length of the path in
the atmosphere required to reduce the luminous flux in a
collimated beam from an incandescent lamp at a colour
temperature of 2,700 K to 0.05 of its original value, the
luminous flux being evaluated by means of the photometric
luminosity function of the International Commission on
Illumination.
© Crown copyright Met Office