Page 1© Crown copyright 2004 Review of Progress in the Development of Operational Upper Air Technology May 2005

© Crown copyright 2004 Page 1

Review of Progress in the Development of Operational Upper Air Technology

May 2005


Introduction to Wind Profilers in the UK

John Nash,

Upper Air Team ManagerObserving Methods Technology Centre,

Technology and Applied Science

Met Office, Exeter, UK

[email protected]


Introduction

Progress will be reviewed for four different types of upper air system

Radiosondes – giving very detailed vertical profiles of temperature, relative humidity and wind

Wind profilers and Doppler weather radars, able to provide continuous monitoring of upper wind given suitable conditions

Microwave radiometers , able to provide continuous monitoring of temperature , water vapour and cloud properties in the lower troposphere, but with certain limits on vertical resolution

GPS measurements of integrated water vapour, able to provide continuous monitoring of integrated water vapour from a large number of sites.


General comments (1)

Groundbased remote sensing offers the chance of measurements at very high temporal resolution, but for temperature and humidity poorer vertical resolution than radiosondes

Is ground based remote sensing developed with research interests in mind or are the systems being moved towards operational applications?

Do operational meteorologists hinder development by lack of consistency in suitable specifications for systems, e.g. Should the customer provide the detailed techcnical specification for his solution, or just the required accuracy of the system ouptut + certain basic technical requirements?

Is the failure to produce many skilled upper air instrument specialists within the NMHS services hindering progress, with poor guidance being provided to manufacturers?


General comments (2)

Operational upper wind and temperature measurements from large commercial aircraft are of similar quality to some radiosonde systems. Relative humidity measurements are starting to become available in the US, see following talk by J. Stickland.

However, radiosonde and ground –based vertical soundings do have a viable future, since there are clearly areas in every upper air network where aircraft will never provide enough operational measurements.

The question of a viable market size for instrument manufacturers [ e.g. for wind profilers] and the impact on unit costs of drastically reducing the number of radiosondes in use should not be ignored by network planners.


Progress with radiosondes [as indicated by WMO High quality radiosonde test, Mauritius]

Small temperature sensors with rapid time constants of response allow daytime solar heating errors to be reduced to less than 1.5 deg C at 10 hPa , on many radiosondes.

At night , temperatures of the best radiosondes agree to within 0.3 deg C, as long as aluminized sensors are used to ensure minimal coupling to the infrared radiation fields.

Many relative humidity sensors now provide consistent results in both wet and dry conditions, with reasonably good agreement in vertical humidity structure down to temperatures of -70 deg C.

Most relative humidity sensors have a day-night bias of at least 5 per cent at high humidity in the tropics , and this problem has yet to be tackled properly.



Temperature and relative humidity compared shortly after launch in Mauritius at night


Temperature and relative humidity compared in the middle troposphere in Mauritius at night


Temperature and relative humidity compared through cloud above 5 km, daytime showing low bias in all sensors apart from the SRS


Temperature and relative humidity compared in the upper troposphere in Mauritius at night


Progress with radiosondes continued

Code correlating winds have good accuracy with low amounts of missing wind data

Radiosonde transmitters are narrow band and much more stable than in earlier generations, so WMO cannot be criticised for wasting spectrum by ITU

This has a by-product in that it is much easier to perform comparison testing with large numbers of radiosondes than in earlier years.

Height assignment errors at pressures lower than 100 hPa from pressure sensor errors can be eliminated by using GPS height measurements


Simultaneous wind comparisons from Mauritius


Simultaneous wind comparisons from Mauritius


Simultaneous geopotential height measurements from GPS sensors


Simultaneous geopotential height measurements from GPS sensors


Current problems [1]

The rapid change over to the new radiosondes is causing problems to many Members. Customers are reluctant to pay the price associated with upgrade. On the other hand manufacturers need to change techniques, e.g. soldering, and must use modern manufacturing technology to minimise production costs.

The customer cannot be expected to pay for endless upgrades , particularly when equipment was purchased as perfectly adequate only a few years ago.

The solution requires serious negotiation between the two parties, or external help from those with the necessary technical background.


Countries that wish to manufacture their own radiosondes

The radiosondes from these countries generally lag behind the measurement quality of the commercially available radiosondes

Better methods need to be devised by CIMO to encourage progress with the new designs currently being prepared for introduction.


How do the wind measurements fit with winds from other systems?

Example from Europe for 28 April 2005

Wind profilers + Doppler radar


10 km 00.UTC


10 km10 km 12.UTC


2 km 00.UTC


2 km 12.UTC


Most recent major expansion of wind profilers in Japan


Map of JMA wind profiler sites


50Winds close to centre of typhoonapproachingmainlandJapan


New generation of profilers in Europeincorporating new hardware and software - DWD Nordholz


Some questions?

Should wind profilers cost as much as weather radars or do they need to be significantly cheaper?

Do wind profilers need to be as accurate as the best radiosondes or can larger random errors be tolerated?

How do users and manufacturers work together to keep costs down?

Are existing wind profilers positioned in the most beneficial localities?


Microwave radiometer

In the last three years the cost of multichannel microwave radiometers has begun to drop from about €400,000 towards

€130,000. In the very long term , this technology may become very much cheaper than this…

The radiometers can provide temperature and relative humidity profile in the lower troposphere, with much less vertical resolution than a radiosonde , but with continuous monitoring.

The radiometers have now been improved with blowers to allow operation in light rain and drizzle. Integrated water vapour measurements are of good quality apart from in heavier rain.

Scan rates of the radiometers have improved so that sampling is now more appropriate for measuring cloud properties such as total liquid water content plus profiles of liquid water,

In the UK, the radiometers have been very reliable in deployment needing little maintenance intervention.


Radiometrics MP3000 Microwave Radiometer

7 Channels: 51-59 GHzO2 band - temp. profile

5 Channels: 22-30 GHzH2O line - humidity, cloud

Infrared Radiometer Pressure, temp., RH sensors Dew Blower & Rain Sensor Automatic Calibration

black body, noise diode

Zenith and Elevation Scans Zenith, ±60°, ±70°, ±75° Observation Cycle: 1 min

Radiometrics MP3000 Microwave Radiometer at Camborne


Surface T

Surface U

Surface p

IR Temp Int. water vapour

Cloud liquid water

Cloud liquid water

95

04

02

Radiosonde measurements


95

08

915 MHz wind profilersignal to noise dependson refractive index gradient

Possibility of improving radiometer profiles being investigated in COST 720


Improved Sample Speed of Radiometrics MP3000 is necessary for cloudy conditions

Data Rate from Radiometrics MP3000For n Views + 1 Black body at ~0.2K noise

1.0

10.0

100.0

1000.0

Jan-02 Jan-03 Jan-04 Jan-05

Sca

ns/

ho

ur

1 view/scan

5 views/scan

7 views/scan


Comparing Retrieved Profiles with Observations

Radiometer

Atmosphere

Radiances

Neural Network

Profile

GHz


CAL. BIAS

RAOB BIAS

SPECTROSCOPY BIAS?

22.2 23.0 23.8 26.2

30.0 51.2 52.3 53.9

54.9

Obs

erve

d –

calc

ulat

ed B

right

ness

tem

pera

ture

[k]

56.7 57.3 58.8


Statistics of Retrieved Profiles

Results from

132 cases 5/11/03-20/1/04 v2.23


Radiometer Physics HATPRO

Filter bank Design – Fast! 22-29 GHz – humidity/cloud 51-58 GHz – temperature Beamwidth: 3.5 at 22 GHz Radiometric noise: 0.3-0.4 K

rms at 1.0 s integration Absolute system stability: 1.0K Thermal stability: < 0.02 K Rain sensor and shutter

(including a dew-blower) Integrated PC on-board GPS clock Pressure, humidity,

temperature sensors Optional IR-radiometer Frequency extension possible

by tandem operation “Low cost”!

Radiometer Physics’ HATPRO

Humidity And Temperature PROfiler


Calibration Differences MP3000-HATPRO

Average Differences between MP3000-Modelled sondes and MP3000-HATPRO in clear skies during HATPRO trial

10/11/04-3/1/05, Camborne (12 cases)Error bars indicate standard errors of averages.

Estimate of HATPRO - Modelled radiosondes


Microwave radiometers will probably be used in conjunction with other sensing systems in future.

The COST 720 Integrated profiling project expects a combination of :-

microwave radiometerlaser ceilometersurface measurementscloud radar

to provide estimates of cloud structure/liquid water content + temperature and relative humidity profiles.

Use with wind profiler/ and or weather radar signals is also to be investigated


Laser ceilometer

COST 720, TUC experiment, Payerne ,November 2003


78 GHz cloud radar


16.01 16.36 16.70 17.05 17.40 17.75 18.09 18.44 18.79 19.13 19.48 19.83

484

686

888

1090

1292

1494

1696

1898

2100

2302

2504

2706

2908

3110

3312

3514

3716

3918

4120

4322

4524

Time [hours] UTC

Height [km]

Signal to noise, range corrected for signals above noise level, High mode,Payerne,30.11.03

55-58

52-55

49-52

46-49

43-46

40-43

37-40

34-37

31-34

28-31

25-28

22-25

19-22

16-19

13-16

10-13

7-10

4-7

1-4

-2-1

-5--2

-8--5

-11--8

-14--11

-17--14

-20--17

-23--20

1.29 GHz profiler signal


GPS water vapour

Needs GPS antenna installed on stable mount with good horizon and minimal multipath reflections, i.e. GPS cannot be readily reflected into the antenna from nearby surfaces, see next slide

GPS receiver must process signals at two frequencies to allow compensation for signal delays in the ionosphere, see following slide

Receiver needs realtime communications to a central processing centre

In order to compute integrated water vapour amount it is essential to measure atmospsheric pressure at the antenna height, and it is helpful


GPS sensor installed by Met Office at South Uist wind profiler site



How to afford a detailed network with spacing between sensors less than 70 km??

Installation of receiver + purchase of receiver costs about £15,000, so it is too expensive for the Met Office to install a widespread network

All wind profilers in the UK have a collocated GPS sensor since the combination of wind + water vapour measurement at high temporal resolution is much more useful than water vapour on its own

UK network has now increased to more than 70 sites , because of a memorandum of understanding with the UK national mapping Agency [Ordnance Survey], where the Met Office hosts some of the Ordnance Survey sensors at some automatic weather station sites. In return Ordnance Survey allow access to the data from all their sites in the UKas collected at the HQ in Southhampton.


The capability of the GPS network across the British Isles is illustrated by hourly measurements associated with a warm and then a cold front crossing the British Isles in April 2005

These measurements were delivered to users 45 minutes after the end of the sample period. Processing was performed at Nottingham University on a system to be reinstalled at the Met Office in May 2005.

The plots are contoured at 2 kg.m-2 intervals, with 21 kg.m-2

corresponding to saturation with respect to water in the warm sector and 17 kg.m-2 to saturation in the colder air.

Random error in the water vapour measurements is expected to be about 1 kg.m-2 corresponding to an average random error in relative humidity of between 5 and 6 per cent at these temperatures


05 April 19.30


05 April 20.30


05 April 21.30


05 April 23.30


06 April 00.30


06 April 01.30


06 April 02.30


06 April 03.30


06 April 04.30


06 April 05.30


06 April 06.30


06 April 07.30


06 April 08.30


06 April 09.30


06 April 10.30


Summary about GPS water vapour

GPS water vapour measurements are not yet handed over to full time operations in any national network.

Whilst improved forecast capability is found using data from pre-operational real time networks in the USA and Europe, evidence of benefit has not always been so strong that all countries performing research are willing to invest in the costs of an operational network.

Costs can clearly be reduced by cooperating with other agencies deploying GPS sensors, e.g. for geodesy, surveying, seismology, tide gauges, marine navigation and other transport and tracking applications.

This system will work well in tropical countries, but probably requires centralised regional processing and measurement distribution to be established through some cooperative program.

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Page 1© Crown copyright 2004 Review of Progress in the Development of Operational Upper Air Technology May 2005