@tobyportugal - artificial intelligence in the form of ChatGPT has explained you somewhat.
If you’ve observed overheating of the Barani Gen III compared to the WMO screen at low solar angles, several design and environmental factors could explain this:
Possible Causes of Overheating in Barani Gen III:
1. Shield Geometry and Plate Design:
The structure of Barani shields may lead to greater absorption of radiation under certain conditions. If the plates reflect or concentrate sunlight onto the sensor, overheating can occur, especially at low sun angles.
2. Material of the Shield:
The materials used in Barani may have a higher radiation absorption coefficient than those in the WMO screen, causing the shield’s surface to heat up and transfer warmth to the sensor.
3. Lack of Passive Ventilation:
At low solar angles and under weak wind conditions, natural ventilation might be insufficient, leading to localized overheating inside the shield.
4. Ground Reflections (Albedo Effect):
Low-angle sunlight may reflect off bright surfaces (snow, sand), increasing the heat load on the shield and causing additional warming.
WMO Screen as a Benchmark:
WMO-compliant screens are designed to minimize the effects of solar radiation, wind, and humidity. If Barani Gen III shows overheating compared to a WMO screen, this suggests that the Barani shield might struggle to manage solar influence effectively in some conditions.
Conclusion:
Your observation confirms that Barani Gen III may have issues coping with low solar angles, leading to overheating. Comparative tests with a WMO screen provide valuable insights into this problem and can highlight when it may be beneficial to use active shields or better-designed passive ones.
Why Use Active Radiation Shields at Commercial Airports?
Active radiation shields are not used at commercial airports for comparison with passive ones but to ensure the highest accuracy and continuity of measurements under various weather conditions. Several key reasons justify their use:
1. Minimizing Measurement Errors:
• Precise meteorological data is crucial for flight safety, especially during takeoffs and landings.
• Active shields reduce the risk of sensor overheating in low wind and intense sunlight conditions, preventing inaccurate temperature readings.
2. Stable Measurements Regardless of Conditions:
• Airports often face changing weather, such as low sun angles, high albedo (snow), fog, or calm winds.
• Active shields ensure a constant airflow, allowing for accurate measurements even under challenging conditions.
3. Redundancy and Reliability:
• Doubling or tripling sensors, including both active and passive shields, provides redundancy. This allows for cross-checking data and identifying anomalies.
• If one method fails, the other can still deliver reliable data, ensuring safety.
4. Adaptation to Local Conditions:
• Different airports have specific needs based on their locations. For example:
• Oslo: Low temperatures, snow, and high albedo increase the need for active shields.
• Madeira: Strong sunlight and variable winds also justify the use of active shields.
5. Regulations and Standards:
• Accuracy requirements for meteorological measurements at airports are regulated by international organizations like ICAO and WMO. Active shields help meet these standards.
Conclusion: Active radiation shields at commercial airports are not a luxury but a necessity. Their presence ensures accurate, reliable, and continuous measurements in all conditions, which is crucial for the safety and efficiency of airport operations.
