European Facility For Airborne Research Nov. 25, 2020, 17:47
Focused on a fundamental measurement – humidity – which is of central interest across a broad range of atmospheric science, the research activity DENCHAR aimed to facilitate new instrumental developments together with extensive testing, both in the laboratory and in-flight, including routine operations within EUFAR (e.g. investigations on the sampling characteristics of different gas/ice inlets and development of an improved ultra-fast thermometer for near- and in-cloud measurements).
In the first two reporting periods (Oct 2008 – Sept 2011) the four new types of hygrometer using different detection techniques as well as the novel ultra-fast thermometer were developed. Parallel laboratory tests of the individual prototype instruments were made at the humidity calibration facilities at FZJ, Jülich. At the end of RP2 the instruments were tested on their in-flight performance during a research aircraft intercomparison campaign (IFCC-2011) in May 2011. All data from the different hygrometers were compared “blind” to those of the advanced airborne hygrometer (e.g. FISH), and all data were stored “blind” before any comparison were conducted. In general, from these tests the different instruments demonstrated good performance over a wide range of humidity levels covering 3 orders of magnitude between 10-50 ppmv up to 30,000 ppmv.
In RP3 (Oct 2011 – March 2013), the work was focused on the preparatory work for the endurance testing (ET) of the instruments integrated in a small flight package during a routine flight operation of a Learjet aircraft. Therefore a small flight package (SFP) was designed and constructed containing all four hygrometers together with a data acquisition system. The SFP can be flown autonomously on any research aircraft.
For the purpose of the planned endurance testing, the SFP had to be flown unattended (no operator aboard the aircraft) during the routine flight operation of a Learjet aircraft. Although the SFP was ready for the endurance testing, its certification was still pending in RP3, such that this sub-task was delayed. It was evident that at the end of RP3, even if the required certification documents had been obtained to fly the SFP unattended on the Learjet, the JRA1 working group would have not been able to accomplish the full nine months of endurance testing within the timeframe of the EUFAR project. Therefore on this deliverable corrective steps had to be taken for the task “Endurance in-flight testing of compact hygrometer package” which was re-defined to “Calibration and In-Flight Validation”. Therefore in the last reporting period, the SFP was flown during two dedicated research flight campaigns (May and September 2013) as part of the AIRTOSS (AIRcraft Towed Sensor Shuttle) experiments. Aboard the Learjet 35A D-CGFD the SFP was thereby operated side by side with the Lyman FISH Hygrometer together with cloud detecting instruments. All data of the hygrometers (incl. FISH) were stored “blind” before any comparison was made. From the intercomparisons the instruments showed very good and consistent performance over a wide range of humidity levels covering almost three orders of magnitudes between 10-50 ppmv up to 20,000 ppmv water vapour mixing ratios. Flight by flight the DENCHAR-instruments demonstrated significant consistent behaviour in comparison with each other and as well as compared to the FISH-reference instrument. Within their uncertainty range (5-10%), all instruments agreed very well and were traceable within about 10% uncertainty to the DP30 (MBW) frost point hygrometer of the ground-based FISH-calibration bench. The results have been evaluated and compiled in an assessment report.