A new airborne tandem platform for collocated measurements of microphysical cloud and radiation properties

摘要

A new airborne tandem measurement platform for cloud-radiation interactionstudies is introduced in this paper. It consists of a Learjet 35A researchaircraft and the AIRcraft TOwed Sensor Shuttle (AIRTOSS), which is aninstrumented drag-body towed by the Learjet. Currently, the AIRTOSS isinstrumented with a Cloud Imaging Probe (CIP) for measuring cloudmicrophysical properties and an Inertial Navigation System (INS) formeasurements of flight attitudes. The cable dragging AIRTOSS can be as longas four kilometres. Thus, truly collocated measurements in two altitudesabove, in, and below clouds can be obtained. Results from first test flightswith Learjet and AIRTOSS are reported here. The flights were performed fromHohn Airport, Germany. Specific manoeuvres were flown to test the aerodynamicbehaviour of the drag-body and to investigate the suitability of AIRTOSS forhigh-precision irradiance measurements which require a stable flight attitudeof AIRTOSS. The flight attitude data show that AIRTOSS is sensitive toseveral flight manoeuvres such as turns, altitude and airspeed changes, andalso to changes of towing cable length. The effects of these manoeuvres onthe attitude angles of AIRTOSS have been quantified. Maximum roll angledeviations were observed during turns. Even small changes in headingcan lead to high roll angles (one degree change in heading causes a change inroll angle of about eight degrees). The pitch angle varies during climb ordive periods, extending or retracting of towing cable, acceleration ordeceleration, and even when flying at too low or too high true airspeeddepending on altitude. Values of pitch angle between −5° (dive) and8° (climb and retracting towing cable) have been observed. Whilechange in attitude is not problematic for cloud particle propertymeasurements it is for radiation measurements. Here, the deviation from thehorizontal should be no more than 3° to avoid large errors. Whenkeeping the above mentioned flight parameters constant, sufficiently stableflight conditions can be maintained to perform high-quality irradiancemeasurements with AIRTOSS in future experiments. During this test campaignalso observations of cloud microphysical data as for example droplet numberconcentrations and size distributions with the AIRTOSS in stratocumulusclouds were performed to prove the compliance with scientific needs.Simultaneous spectral cloud radiation measurements have been made. Themeasurements of internal operational data of AIRTOSS as well as the firstatmospheric data demonstrate the suitability of this tandem platform fordetailed cloud microphysics and radiation interaction studies.