World Meteorological Organization

Joint Session of the Expert Team on Operational In Situ Technologies (ET-OIST) and the Expert Team on Developments in In Situ Technologies (ET-DIST)Geneva, Switzerland, 21-23 June 2017

CIMO/ET-A1-A2/Doc. 8.4 Submitted by:

Guo Jianxia15.6.2017

GUIDELINES FOR INSTRUMENTS AND MEASUREMENT INFRASTRUCTURE IN EXTREME ENVIRONMENT

Summary and purpose of document

This document provides information on the guidelines for instruments and measurement infrastructure in extreme environment (based on CIMO GUIDE Annex 1.D).

ACTION PROPOSED

The Meeting is invited to review and extend the document. ________________

Appendix I: Report of the technical explorations for surface observation withstanding severe weather in coastal areas of China

CIMO/ET-A1-A2/Doc. 8.4, p. 1

1 Background

This task is derived from sections 9.28-9.32 of CIMO-XV session (WMO-No. 1064), which references the WMO Disaster Risk Reduction (DRR). The disasters can have impacts on observing networks leading to interruption of the core functions of National Meteorological and Hydrological Services (NMHSs), including observations, monitoring, forecasting and warning services. The WMO DRR country-level survey (2006) indicated that droughts, flash and river floods, strong winds, severe storms, tropical cyclones, storm surges, forest and wild land fires, heat waves, landslides and aviation hazards were the top ten hazards of concern to all Members. Maintenance of high quality observational records (historical and real time) is critical for DRR applications, including: (i) risk identification; (ii) risk reduction through the provision of early warnings to support emergency preparedness and response as well as climate services for medium- and long-term sectoral planning; and (iii) risk transfer through insurance and other financial tools. Thus, interruptions in monitoring caused by damages to instruments and observing networks as a result of natural hazards, hamper NMHSs capacities in delivering effective services not only during and following a disaster, but also in the long-term, if these systems are not rebuilt. In this regard, the Commission stressed that it is critical to ensure that instrumentation and observing networks are designed per standards that would withstand the impact of extreme weather events. ET-A2 started the work of providing guidance for observations in extreme weather events during the CIMO-XV to the CIMO-XVI session. The working documents “Operating equipment in extreme environments” was accepted as the Annex 1.D to the 2014 version of CIMO GUIDE. China has practiced some technique in the coastal areas (see Appendix I of this document).

2 Operating Equipment in Extreme Environments (Annex 1.D of CIMO GUIDE)

2.1 Extreme winds (tornados, hurricanes):

Aerodynamic shapes can be used to improve the survivability of instruments and structures. Weighted shaped disks on the ground can help keep instrumentation in place during tornados. Shaped balloons can enable tethersonde operation in hurricane-force winds. Masts can have additional stays fitted. All cabling should be well tied down and supported.

Shielding should be put in place to protect equipment from wind blown debris, for both large objects (that can cause impact damage) and smaller particles like dust and sand (that can cause erosive damage).

Anemometers using the measurement principle of pressure difference and Anemometers and Vanes using the principle of sound propagation (ultrasonic wind sensors) eliminate the vulnerabilities associated with moving parts. Nevertheless, some types of cup and propeller anemometers can operate during extreme wind events.

2.2 Flood and Storm Surge:

Sites should avoid low-lying areas. Sensors can be raised on pilings to prevent damage due to surface water flow and debris. Foundations using resilient materials should be used and be oriented parallel to any expected surface flow to minimize hydrostatic pressures. Electrical connections should be raised above predicted flood levels or contained within suitable waterproof housings (designed to suitable IP ratings).

2.3 Fire:

Non-combustible materials, generally metal and concrete, should be used wherever practicable. Equipment openings should include screening to prevent sparks from entering cavities - as long as measurement exposure will not be compromised.

2.4 Icing:

CIMO/ET-A1-A2/Doc. 8.4, Appendix I. 2

Heat and/or air flow over sensors is commonly used to keep sensors free of ice. Some manufacturers include built in sensor heating with varying heat amounts depending on expected icing severity. Sensors without built in heating can still be heated by applying "heat tape" directly to surfaces (electrical resistance elements embedded in a flexible sheet or by use of nichrome wire). Note that for wind sensors it is generally easier to heat those with no moving parts (e.g. ultrasonic wind sensors). Another method is to spray a low-freezing point fluid (e.g. ethanol) on sensors during icing events. In heavy icing conditions, none of these methods may prevent ice build-up.

Icing on mounting structures can disturb the air flow and measurement environment even when the sensors themselves are ice-free. Minimizing the surface area of these structures can help. Deicing of the supports themselves also may be necessary.

It should be remembered when applying methods to mitigate ice accretion that the method used should not affect the sensor measurement or the measurements being made by adjacent sensors e.g. heating of a sensor must not affect nearby air temperature or relative humidity measurements.

2.5 Solar Radiation Heating and Erosion:In locations where sensors, cabinets and cabling receive high levels of solar radiation, and in particular high levels of Ultra-Violet (UV) exposure, some materials will rapidly break down and begin to “weather” away. The use of alternate materials like metals, hard-woods and UV stabilised plastics will often achieve much greater equipment and structure lifetimes.

In warmer climates and where here are receive high levels of solar radiation eluent cabinets can heat up internally to extreme levels which exceed the operating specifications of equipment thereby compromising data values and equipment reliability. The use of vents and/or forced venting (with appropriate filters), or small air condition systems can be employed to reduce heat build up.

The use of solar shades, cable conduits or simply burying equipment can also be used where sensor measurement exposure will not be compromised.

2.6 Electrical Transients:In locations with high risk of direct lightning strike equipment installed at higher locations than the general surrounds e.g. wind sensors and radio antenna, are more vulnerable. The use of “Lightning Rods” or “Lightning Air Terminals” can be employed to divert lightning away (i.e. capture and conduct it to ground). The conducting cables should be as of sufficient capacity, highly conductive and as straight as possible, and connect to a suitably low impedance earth (Earth rod or rods or mat). Screened cables, earthed at one end only, should also be used to reduce the likely hood of induced transients in signal lines.

For equipment that connects to third party infrastructure e.g. telephone lines and mains power lines, or uses power from generators, or has long cable runs between sensors and modules, there is the risk of direct or induced electrical transients in cables. The use of appropriate transient protection and/or isolation devices where cables enter equipment, and at both ends of long cables is recommended. Careful attention must be made when earthing transient protection devices so that “Earth-Potential-Equalisation” is achieved for each system being protected.

2.7 Corrosion (High Salt, Geothermal and Humidity Environments):Equipment installed in locations with high or moderate corrosive atmospheres can suffer from data errors due to sensor malfunction and reduction in equipment reliability.

Common problems include: Foreign chemical build up on sensing elements e.g. Relative humidity sensing

elements; High friction in sensor bearings; Seized bearings, hinges, latches, screws and terminals; Mold and corrosion on circuit boards; High resistance terminal connections;

CIMO/ET-A1-A2/Doc. 8.4, Appendix I. 3

Structural failure of mounts and clamps.

Mitigating strategies should include: Use of suitable materials e.g. Stainless steel, galvanised steel, appropriate plastics; Protection of connectors and clamps using grease/oil impregnated tape or similar; Careful selection of metal types at joints or use of isolating separators and lubricants

(high viscosity grease) to ensure electrolysis is minimised;

2.8 Security (Against Human or Wild Life Interference):Tampering and theft of equipment can be minimised by installation of appropriate security structures e.g. protective fences, or by the installation of non-removable fittings so that high value modules like solar panels can not be removed without having the appropriate keys or tools.

Some soft infrastructure like plastics and cable sheaths are vulnerable to attach by wild life e.g. chewing of cables by birds. This can be mitigated by the use or armored cables or enclosing cables in toughened conduit.

Physical crushing or misalignment of sensors due to rubbing of sensors and structures by large animals can be mitigated through the use of appropriate livestock fencing.

2.9 Loss of Infrastructure:During extreme weather and geophysical events mains power may become unavailable for many days. Appropriate battery backup design should be made so that equipment will continue to operate until power is restored or workers can visit a site and replace batteries.

During extreme weather and geophysical events telecommunications networks may become inoperative or overloaded for many days. Outages may only affect one operator so the use of diverse communications via separate operators and separate communications path may be a useful option e.g. having both cellular and satellite communications at a station.

2.10 General:

Regular maintenance as described in 1.3.5 will increase the survivability of structures to extreme events.

Redundant data communication paths reduce the risk of data loss during extreme events. Similarly, redundant and/or quick-deploy systems can supplement damage from extreme events.

Characterization of instrument response to extreme events may enable data to be used even when operating beyond manufacturer specifications and is to be encouraged whenever possible. Post calibration of damaged sensors may enable recovery of data through extreme events.

Adherence to these guidelines does not guarantee network operation through extreme events. Human operators can reduce data loss, though extreme conditions often are associated with high risk to human life. Some amount of data loss in these conditions is expected.

CIMO/ET-A1-A2/Doc. 8.4, Appendix I. 4

Appendix I

REPORT OF THE TECHNICAL EXPLORATIONS FOR SURFACE OBSERVATION

WITHSTANDING SEVERE WEATHER IN COASTAL AREAS OF CHINA

Jianxia GUO, Zhichao Wang, Bailin Wang, Xin Zhang and Dongdong ChenMeteorological Observation Center of CMA, Beijing, China

China has a long coastline, and is one of the worst affected countries by typhoons. According to statistics, for the last 15 years (2000-2014), a total of 113 numbered typhoons landed for 163 times in coastal areas of China, an average of 7.5 typhoons for 10.9 times landed in coastal areas of China each year. Strong wind observations on the surface can reflect the wind speed and direction before and after the typhoon landing, which could provide important meteorological observation data for severe weather now casting.

 

Figure 1 typhoon tracks in China in recent years

However, in continuous high-temperature, high-humidity, high-salt and strong wind conditions, the wind sensor observation stations along the coast and islands prone to failure or damage, and the equipment failure rate is very high. And they cannot guarantee the normal meteorological observation during the landing of typhoon. The main causes are:

①in high-temperature, high-humidity, high-salt conditions, the capability of anti-wind and anti-corrosion for wind sensors in coastal areas is weak and reduce its service life for strong wind observation.

② the maintenance of strong wind sensor is difficult, which makes equipment support personnel cannot ensure timely and regular maintenance.

③ the performance of some strong wind sensors is bad, prone to damage for wind-cups or propellers in continuous strong wind conditions.

The common problems are mainly categorized:1) Damage of wind speed sensors: wind sensors, sensor connectors, bearings, supports,

wind lever / wind towers, cable and other equipment are susceptible to corrosion in high-temperature, high-humidity, high-salt conditions, resulting in damage to the sensor.

CIMO/ET-A1-A2/Doc. 8.4, Appendix I. 5

Figure 2 wind-cups and wind lateral arms broken due to serious corrosion

2) Damage or deformation of the wind speed sensor. In the strong wind conditions in coastal areas, the wind-cups and the propellers are of the most vulnerable equipment, which can be easily torn off from sensor components or deformed.

Figure 3 damage of a wind speed sensor and a link cable

Figure 4 junction fracture of the wind lateral arm and wind tower

3) Damage of wind sensor components. The wind lever and cable have potential danger in the long term field service. The cable will break in the strong wind condition and result in the damage of wind lever.

CIMO/ET-A1-A2/Doc. 8.4, Appendix I. 6

Figure 5 a broken wind lever pulled off by the wind sensor connection cable

4) Many components need frequent replacement because of serious corrosion (Figure 6).

Figure 6 serious corrosion in coastal areas (corroded welding point, screw, and rain barrel in sequences)

In order to prevent damage to the surface observing systems, the meteorological stations in coastal areas of China made some exploration.  The following methods were found to be useful for preventing damage to the wind sensors:

1. Smear butter to junction components for anti-corrosion

Weld joints and screws are susceptible to corrosion and the corrosion will accelerate once rust produced. The fixation ability and anti-wind capability will be tremendously affected when some components corroded. Hainan meteorological administration applies butter smearing to fixed points for the wind lever at a national meteorological surface observing system (Figure 7). One observation station was butter smeared every three days for important junction components, and greatly reduce corrosion by the narrator (Figure 8).

CIMO/ET-A1-A2/Doc. 8.4, Appendix I. 7

Figure 7 butter smearing for anti-corrosion

Figure 8 butter smearing for each joint point for sensors

2. Radiation protection with breathable, non-reflective canvas

The severe solar radiation causes rapid warming for surface observing systems, and has great impact on the components. Figure 9 shows the applying of breathable, non-reflective canvas to reduce the impact of solar radiation for a better service life.

Figure 9 radiation protection by breathable, non-reflective canvas

CIMO/ET-A1-A2/Doc. 8.4, Appendix I. 8

3. Enhance the anti-wind capability for the wind lever using high strength nylon and new fixing methods

The wind lever and the wind sensor mounting bracket are the most vulnerable components after typhoon passed. The cable for fixing wind lever in most Chinese surface observing systems are metallic. And the metal cable is vulnerable by corrosion in the high-temperature, high- humidity and high-salt conditions, which leads the damage of the wind lever.

Many attempts have been made for wind lever fixing method in Hainan province. First of all, high strength nylon was used to reduce the potential corrosion (Figure 10a).Second, a four cable fixing method was applied to prevent instability after one of them broken (Figure 10b). These two new methods are still on the experimental stage, especially for the capability of anti-corrosion and anti-radiation with new materials. The methods could be popularized to other surface observing systems in the coastal areas if it works.

a) The high-strength nylon b) four pull rod fixing methodFigure 10 an attempt to improve anti-wind capability for the wind lever

4. Upgrade the wind sensor mounting bracket and fixation method

The wind lateral arms and mounting brackets of wind sensors in the coastal areas are easily corrupted and vulnerable in the strong wind condition, resulting in the loss of data. An embrace hoop method was applied to fix the wind sensors in some surface observing systems, and reduced the potential damage to some extent.

Figure 11 wind sensors mounted on the wind lever by the embrace hoop method

CIMO/ET-A1-A2/Doc. 8.4, Appendix I. 9

In the future, research should be made for better fixation method and new mounting brackets as well as the performance of strong wind sensors. In addition, other methods for enhance the anti-wind capability are in experiment:

1) Improvement for the wind-cup manufacturing materials. The applying of Carbon fiber (MPP0 20% glass fiber) makes the once-forming wind-cups and holders with no rivets, in order to improve the tensile strength for wind sensors.

2) Improvement of machining accuracy for the bearing pedestal. If the gap increases as the outer diameter of the bearing unchanged, it will do good to heat dissipation in high-speed rotation of bearing, and effectively improve the service life of bearing by preventing uneven heating. Then the applying aluminum alloy 2A12 as bearing pedestal manufacturing materials would improve the tensile strength.

3) Improvement of wind lateral arms by using new raw materials and surface treatment technology. By improving the tensile strength and anti-corrosion of the lateral arm, fixing steadily the wind lateral arm and the wind lever by the connecting parts, the wind lateral arm shall not fall easily.

4) Strengthening fixation of the wind sensor and the wind lateral arm. The anti-looseness of screw thread, deepening the fixing groove of the lateral arm, and the installation of the lock nut would enhance the anti-wind capability of wind sensors.

8, Nov, 2015