Sounding Data Continuity

• In cover improvement, the hard plastic covers of RS41 have been changed to EPS (expanded polystyrene) covers.
• Regarding sounding operations and radiosonde measurement performance, the cover improvement applied to RS41 radiosonde does not involve any changes, but this is a significant change from the environmental point of view.
• With the improved covers, the plastic content of RS41 is decreased by 47% and the weight by 27% when compared to the hard plastic cover version.
• The comparison flight data is published on the white paper showing that the change does not have any impact on the measurement performance of RS41.

• The 2D code location is changed on the sensor boom to improve the manufacturability
• As a consequence of the location change, the shape of the sensor boom is less steep than in the booms with the old 2D code location
• Modification has no effect on temperature or humidity measurement as the surrounding of the sensors have not changed at all
• The change of the 2D code location can be identified with help of radiosonde serial number

Vaisala BioTwine™ available as an option for RS41-SG and RS41-SGP – No data continuity effect

• Vaisala BioTwine™ is a biodegradable twine (unwinder cord) that reduces micro-plastics originating from soundings operations.
• The comparison flight data is published on the White paper proving that the measurement accuracy of the RS41 radiosonde is not affected by the change in the string material.
• BioTwine is available as an option in RS41-SG- and RS41-SGP- configurations.
• The radiosondes with BioTwine can be easily identified with the label in shipping box, but later also with help of the radiosonde serial number.
• In the picture below, an unwinder with Vaisala BioTwine™ (on the right) and unwinder with traditional PP-string (on the left). 
• The White paper is available on request.

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• Vaisala Radiosonde RS41 E-models with Vaisala BioCover™ and BioTwine™ combine high-quality atmospheric sounding data with innovative, biodegradable materials.
• The comparison flight data is published in the technical paper showing that the change does not have any impact on the measurement performance of RS41.
• The radiosonde models with BioCover and BioTwine are RS41-SGE and RS41-SGPE being also identifiable with help of the radiosonde serial number.
• With BioCover and BioTwine, the plastic content of RS41 is decreased by 66% when compared to standard version.
• In the picture below, RS41 with BioCover and BioTwine (on the left) and standard RS41 with standard unwinder (on the right).

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• The height reported in soundings with RS41-SGP is changed to be calculated based on the filtered pressure sensor data
• The previous calculation of the height used the raw pressure data from the RS41-SGP pressure sensor resulting in oscillation of the height values
• The change decreases the oscillation of the calculated height values, and has no bias effect
• Vaisala recommends that customers using RS41-SGP update their MW41 software to version 2.16 or later to decrease the oscillation of the height values

• The reported humidity values in DigiCORA software use improved algorithm for the humidity sensor time lag correction.
• The change decreases the overshooting of the humidity values, in the fast step-like humidity changes that may occur in the sounding, such as during the rapid drying around the tropopause.

• Correction in DigiCORA software improves the temperature measurement in the descending sounding phase when radiosonde is descending at high speed in relation to ambient air. The effect is most predominant right after the balloon burst and before the parachute opening.
• The corrected descent phase temperature also improves the accuracy of the descent phase GNSS based pressure which is integrated using the ambient temperature as one input data.
• More on the phenomena can be read from https://amt.copernicus.org/articles/15/165/2022/amt-15-165-2022.pdf

• Correction in DigiCORA software improves the sensor pressure measurement in the descending sounding phase when radiosonde is descending at high speed in relation to ambient air. The effect is most predominant right after the balloon burst and before the parachute opening.
• The corrected descent phase sensor pressure also improves the accuracy of the descent phase height (GEOPOTENTIAL_HEIGHT in SSD) which is calculated using sensor pressure as an input in hydrostatic equation.

• The reported wind data values in DigiCORA software use improved algorithm for the wind data filtering at descent phase.
• The previous filtering for the wind was over-smoothing at high descent speeds and under-smoothing in conditions when the horizontal movement is strongly dependent on the defective parachute or balloon remnants.

• Correction in DigiCORA software improves the temperature measurement in the descending sounding phase when radiosonde is descending at high speed in relation to ambient air. The effect is most predominant right after the balloon burst and before the parachute opening.
• The corrected descent phase temperature also improves the accuracy of the descent phase GNSS based pressure which is integrated using the ambient temperature as one input data.
• More on the phenomena can be read HERE

• Correction in DigiCORA software improves the sensor pressure measurement in the descending sounding phase when radiosonde is descending at high speed in relation to ambient air. The effect is most predominant right after the balloon burst and before the parachute opening.
• The corrected descent phase sensor pressure also improves the accuracy of the descent phase height (GEOPOTENTIAL_HEIGHT in SSD) which is calculated using sensor pressure as an input in hydrostatic equation.

• The reported wind data values in DigiCORA software use improved algorithm for the wind data filtering at descent phase.
• The previous filtering for the wind was over-smoothing at high descent speeds and under-smoothing in conditions when the horizontal movement is strongly dependent on the defective parachute or balloon remnants.

• Improved temperature dependency correction for humidity measurement
• In production since April 6, 2004
• Old data can be corrected to correspond to new data by:

  

  where:
  Um = measured humidity  
  US = saturation humidity
  dUS = humidity correction at saturation
  dU0 = humidity correction at 0% RH

• ​A sensor that has gathered ice cannot measure humidity profile details accurately in the lower atmosphere. In the upper atmosphere it shows a too high humidity reading
• Vaisala Radiosonde RS92 has two thin film humidity sensors. While the other sensor measures humidity, the other one is heated. The heating functionality reduces icing and condensation effects on the sensor. This results in reliable humidity measurements also when emerging from a cloud
• When the Vaisala Radiosonde RS92-SGP was first released, the alternate heating was turned off when the radiosonde reached -40°C temperature. Since March 2005 the heating functionality has been continued to temperature -60°C. This functionality was also used in the WMO radiosonde intercomparison in Mauritius in 2005. The change leads to more reliable humidity measurements in soundings where there are high humidity conditions between temperatures -40°C and -60°C

Improved attachment decreases warming caused by solar radiation.

• Relative humidity is a function of humidity and temperature
• In daytime soundings, the humidity sensors and their contacts are warmer than the surrounding air they are measuring. This results in too low relative humidity values.
• The effect is noticeable in the upper troposphere and lower stratosphere, especially at high humidity conditions. There the radiosondes with the improved coating measure up to 5-6 %RH higher humidity values compared to those with the old coating.
• The new coating was used in the WMO Intercomparison of High Quality Radiosonde Systems in Mauritius, 2005

• Quartz fibre is integrated firmly into the sensor structure
• This improves mechanical strength by a factor of 5
• Boom frame absence improves sensor ventilation compensating for increased thermal mass and sensor surface
• Boom frame removal reduces temperature fluctuation previously present in twin-soundings
• More details of the phenomenon: Temperature filtering above 10 hPa in heavy rigging
• Reinforced sensors delivered since 2007, sensor type can be identified with help of radiosonde serial number

Temperature Sensor Construction

Time Constants of Old and Reinforced Sensors

• The back side of the sensor boom has changed to a shiny silver like the front side of the sensor boom
• The change improved manufacturability: boom is easier to handle in manufacturing processes resulting in better yield and more equal quality
• No effect on temperature measurement as the surrounding of temperature sensor have not changed at all
• The effect on humidity is positive – if any. In test flights the difference was with-in reproducibility limits
• Modification entered production in mid 2008. If needed, coating method can be identified with help of radiosonde serial number

• The sensor boom contacts have been coated with gold instead of copper to make contacts more robust, e.g., against ageing
• The change improved also manufacturability: boom is easier to handle in manufacturing processes resulting in better yield and more equal quality
• Modification has no effect on temperature or humidity measurement as the surrounding of the sensors have not changed at all
• Modification entered gradually into production in autumn 2010. If needed, contacts used in the boom can be identified with the help of the radiosonde serial number

Sensor Boom Contacts Modification Front

Sensor Boom Contacts Modification Back

Radiation correction table RSN2005 

• Fine-tuned radiation correction table for Vaisala Radiosonde RS92
• The new radiation correction was verified in the WMO Mauritius Radiosonde Intercomparison, February 200

Solar radiation correction table RSN2005​

NOTES: 

• The corrections in the RSN2005 table as a function of pressure and sun elevation angle are shown in the table above
• The corrections are subtracted from the measured temperature

Difference between RSN2005 and RSN96 tables

NOTES:

• The difference between the RSN2005 table and the original RSN96 table as a function of pressure and sun elevation angle is shown in the table above
• Mostly the correction has increased, and thus the effect of the change is to decrease reported temperatures and consequently lower calculated heights
• Below 100hPa the change is less than 0.05 °C and above 30hPa about 0.2 °C

• It has been common practice for many meteorological services to exclude humidity data from TEMP messages at low temperatures. The most commonly used cold temperature limit has been –40°C and it has been applied regardless of sensor design
• Over the years, Vaisala has continuously improved its polymer based humidity sensor. The performance was already improved significantly with the Vaisala Radiosonde RS80 types. However, the Vaisala Radiosonde RS92 family finally provided a sensor quality which allowed Vaisala to recommend the removal of the temperature limit completely
• Vaisala recommended that users of RS92 radiosondes change the temperature limit to –100°C and users of RS80 change the limit to –70°C
  • New Temperature Limit for Humidity Data Reporting in TEMP Message (pdf, 53KB)

• ​The movement of a radiosonde suspended under a test flight rig used in various sounding test campaigns is not the same as that experienced by an individual radiosonde in flight (rigged directly to a balloon)
• The slower movement can cause excess temperature reading fluctuation, ie. the temperature sensor gets warmer than the ambient air for short periods of time. This is observed only at very high altitudes
• The same phenomenon takes place with ozone soundings, since the ozone sounding set-up is much heavier than the normal RS92 radiosonde
• The software used for filtering the raw observations into the reported values was modified to take into account the requirements for slow movement in ozone soundings and in rig test arrangements  
• For further information, please refer to the Final Report of the WMO Intercomparison of High Quality Radiosonde Systems in Mauritius, 2005

• Humidity measurement algorithm has been improved to take into account sensors response time and sensor's heating by solar radiation, latter indicated formerly as dry biased humidity readings at high altitudes.
• The algorithms' biggest impact is in day time soundings at altitudes of approximately ten to fifteen kilometers depending on the humidity profile and tropopause height.
• The new algorithm was used in the WMO Radiosonde Intercomparison, Yangjiang, China, July 2010.
• Note! Applicability of the algorithm is presented in the table "Vaisala Radiosonde RS92 technical change".
• Instructions for simulating the old database files with the DigiCORA® software version 3.64 can be found in the following document: Improved calculations MW31 3.64

Effect on Integrated water vapor column example, tropical conditions

• 17 day soundings and 18 night soundings included
• Day soundings average with new algorithms is 59.3 kg/m2 and with old algorithms 57.4 kg/m2
• Night soundings average with new algorithms is 60.4 kg/m2 and with old algorithms 60.4 kg/m2 

Sounding example, tropical conditions

Sounding example for solar radiation algorithm
Blue = relative humidity with solar radiation algorithm and response time algorithm
Grey = relative humidity without new algorithms
Day time sounding (tropical conditions)

Sounding example, high latitude conditions

Sounding example for solar radiation algorithm
Blue = relative humidity with solar radiation algorithm and response time algorithm
Grey = relative humidity without new algorithms
Day time sounding (high latitude conditions)

Sounding series statistics example, tropical conditions

Comparison result between new and old calculation. Statistics of day time flights in tropical conditions, 20 flights
Blue = relative humidity with solar radiation and response time algorithms
0 %RH reference line = relative humidity without new algorithms

Sounding series statistics example, high latitude conditions

Comparison result between new and old calculation. Statistics of day time flights in high latitude conditions, 50 flights
Blue = relative humidity with solar radiation and response time algorithms
0 %RH reference line = relative humidity without new algorithms
 

• Flight reproducibility test verifies the agreement between similar types of radiosondes when measuring the same atmospheric conditions. Based on the test results the new SW-based corrections, when being effective, also maintain the high level of reproducibility characteristics of Vaisala RS92 Radiosonde humidity sensor.

Reproducibility in sounding

Twin sounding differences with standard deviations using new algorithms, high latitude conditions. 
Left  = Day time, 25 flights
Right = Night time, 5 flights

• Small changes for Vaisala Radiosonde RS92 solar radiation correction table have been made. In addition solar radiation correction algorithm takes now into account radiosonde ventilation during the flight.
• The new correction table was used in the WMO Radiosonde Intercomparison, Yangjiang, China, July 2010.
• Note! Applicability of the algorithm is presented in the table "Vaisala Radiosonde RS92 technical change".
• Instructions for simulating the old database files with the DigiCORA® software version 3.64 can be found in the following document: Improved calculations MW31 3.64

Temperature sensor solar radiation correction table RSN2010

NOTES:

• RS92 solar radiation correction table RSN2010 for DigiCORA® Sounding Software version 3.64
• The correction values in the table are as a function of pressure and sun elevation angle. Actual correction takes into account radiosonde ventilation in flight, presented table values are calculated for typical 5 m/s ventilation.
• The corrections are subtracted from the measured temperature.

Temperature sensor solar radiation difference table RSN2010 - RSN2005

Sounding series statistics example: day time, tropical

Daytime differences with standard deviations between new and old calculation (RSN2005). Statistics of day time flights in tropical conditions, 20 flights.

Blue = new calculation 
Reference line = old calculation
Average ascent rate 5.3 m/s, std. 0.4 m/s. Single soundings, length of string 30 meters.

Sounding series statistics example, night time, high latitude

Night time differences with standard deviations between new and old calculation (RSN2005). Statistics of day time flights in high latitude conditions, 30 flights

Blue = new calculation
Reference line = old calculation
Average ascent rate 5.2 m/s, std. 0.2 m/s. Single soundings, length of string 30 meters.

Flight reproducibility test verifies the agreement between similar type of radiosondes when measuring the same atmospheric conditions. Test proves that reproducibility remains at good level. 

Reproducibility in sounding

Twin sounding differences with standard deviations using new calculation, high latitude conditions, 25 flights.
Average ascent rate of soundings is 5.3 m/s, std. dev. between soundings is 0.3 m/s. Length of balloon string is 50 meters.