Instrumentation on the BAS Twin Otter

The following instruments will be used aboard the Twin Otter during the EUREC4A compaign:

Instrument Description
Total Temperature Goodrich Rosemount Probes are mounted on the nose: A non de-iced model 102E4AL and a de-iced model 102AU1AG are logged at 0.7Hz.
Altitude and Air Speed Static and Dynamic pressure from the aircraft static ports and heated pitot tube are logged using Honeywell HPA sensors at 5Hz.
Cooled-Mirror Hygrometer A Buck 1011C cooled mirror hygrometer is fitted. Chamber pressure and mirror temperature are recorded at 1Hz. A Rosemount mounted Vaisala Humicap sensor is also logged.
Radiometers Eppley PIR and PSP sensors fitted to the roof and underside of the aircraft. Logged at around 10 Hz.
Infra-red Thermometer Heimann model KT19.82 infra-red thermometer mounted in the floor hatch panel. There is a solenoid-operated, ambient temperature, black-body calibration target that can be brought into view during flight. Data are recorded at around 10Hz.
Laser Altimeter A Riegl LD90-3800VHS-FLP Laser Altimeter is fitted in the floor hatch. Returns up to a few hundred metres are possible depending on the surface at repetition frequencies up to 2 kHz.
Cameras Two digital video cameras are installed one downwards looking mounted in the camera hatch, one forward looking mounted in the cockpit.
Radar Altimeters Data are recorded from the aircraft's two radar altimeters at around 10Hz. These have a range of 1000m with a wider beam compared to the laser altimeter.
Turbulence Probe The NOAA/ARA BAT 'Best Aircraft Turbulence' probe is fitted on a boom extending forward from the roof of the aircraft. This 9 hole probe records pressures and exposed thermocouple temperatures for measuring turbulence by eddy covariance in conjunction with attitude measurements. 3-axis accelerometer data are also recorded from the BAT Probe. Heaters are fitted inside the hemisphere to enable the instrument to be usable even after encountering icing.
GPS Position There is a position accuracy of about 5m recorded at 10Hz from the JAVAD 4-antenna GPS attitude system. For greater accuracy this is supplemented by a Trimble 5700 survey system using an antenna mounted above the laser altimeter and processed in kinematic mode with a second ground based unit.
Inertial Attitude and reference Systems An OXTS Inertial+ GPS linked inertial Measurement Unit (IMU) provides attitude and position information at 20Hz.
Wing Hardpoints Both wings have hardpoints, zivko carbon fibre pylons and cabling to accept a total of 4 PMS footprint instruments.
Closed Path water vapour and CO2 sensor The LICOR LI-7000 is a closed path infra-red gas analyser. Sampling is from a Rosemount inlet and readings are triggered at 50 Hz.
Aerosol Inlet The Brectel Model 1200 Isokinetic Inlet is greater than 95% efficient for 0.01 to 6μm.
Condensation Particle Counter The TSI 3010 CPC can sample aerosol particles between the range of about 10 nm to greater than 3 um.
Aerosol Spectrometer A Grimm model 1.109 portable aerosol spectrometer has 31 channels ranging from 0.25μm to 32μm.
Cloud Condensation Nuclei Counter (CCN-100) A DMT single-column cloud condensation counter model measures the spectrum of CCN concentration as a function of supersaturation continuously using uninterrupted flow and a multichannel, optical particle counter that measures the size of the activated droplet.
Scanning Mobility Particle Sizer (SMPS) A TSI SMPS comprising of an electrostatic classifier (3082) and a condensation particle counter (3775) is capable of measuring aerosol particles from a few nanometres up to a micron.
Central Logging System All instruments are logged to a single rack PC using Labview and associated National Instruments hardware including networked compact Fieldpoint modules in the roof and floor. The logging can be monitored and controlled from the main rack in the cabin as well as a remote touch screen in the co-pilot's seat.
SPEC-2DSIn Situ Stereo Cloud Particle Imager The 2D Stereo (2D-S) instrument is an optical imaging probe that provides cloud particle images, size and concentration. Shadows from particles illuminated by two orthogonal laser beams fall onto the two linear 128-photodiode arrays (10 micron resolution). The sample volume is approximately 10 L s-1*. The probe is mounted in an under-wing pod. The measurements include: Particle size (10 to 1280 µm), concentration and shape and derived liquid (or ice) water content. (Instrument Team: Gallagher/Dorsey/Bower, UoM)
SPEC HVPS-3 In Situ Cloud Particle Imager The High-Volume Precipitation Spectrometer (HVPS-3) detects shadows of particles on a single optical linear photodiode array with 128 channels of 150 µm pixel resolution, giving a sizing range up to 19,200 µm. The HVPS-3 uses the same photodiode array and electronics as the 2D-S. The sample volume is approximately 72 L s-1*. The probe is mounted in an under-wing pod. The measurements include: Particle size (150 µm to 19.2 mm), concentration and shape; derived liquid water content. (Instrument Team: Choularton (PI)/Crosier/Bower/Dorsey, UoM)
SPEC F-FSSP-100 In Situ Cloud Probe The Fast-Forward Scattering Spectrometer Probe (F-FSSP) is based on the original design of Knollenberg, and modified to produce high-rate measurements. Single particles are detected by measuring the intensity of light that the particle scatters in the forward direction when passing through a laser beam. The sample volume is 0.02 L s-1*. The probe is mounted in an under-wing pod. The measurements include: High speed (50-100 Hz) droplet size (1.5 to 50 µm diameter) and concentration; and derived liquid water content. (Instrument Team: Bower/Dorsey/Gallagher, UoM).
DMT-CAPSDMT CIP-25 Cloud ProbeDMT CASCloud-Aerosol Probe The Cloud Aerosol and Precipitation Spectrometer (CAPS) is a combination of a hot-wire liquid water content instrument, a Cloud and Aerosol Spectrometer (CAS) and a Cloud Imaging Probe (CIP). Particle sizes from approx 0.5 μm to 1600 µm, can therefore be measured with a single instrument, minimizing space requirements. The instrument is mounted in an under-wing pod. (The hot-wire instrument Liquid Water Content instrument will not be used.) The individual components of CAPS to be used are described below. 1) Cloud Imaging Probe (CIP-25): Shadows of particles passing through a collimated laser beam are projected onto a linear 64-element photodiode array with 25 µm resolution. The sample volume is approximately 10 L s-1. The measurements include: particle size (25 to 1600 µm), concentration and shape, and derived liquid and/or ice water content. 2) Cloud Aerosol Spectrometer (CAS): an optical scattering instrument configured to measure aerosols and cloud particles in the same manner as the F-FSSP/CDP. The sample volume is 0.015L s-1. The measurements include: Aerosol and cloud-drop sizes (0.5 to 50 µm diameter) and concentration, particle refractive index and phase.
DMT Cloud Droplet probe (CDP-100) The DMT Cloud Droplet Probe (CDP-100) is an optical particle spectrometer that measures the concentration and size distribution of cloud droplets. The instrument is similar to the F-FSSP. Measurements are usually provided at 1 Hz in the standard data files but can be made available at 10 Hz in special high-rate processing. The sample volume is 0.015 L s-1*. The instrument is mounted off-fuselage below the nose cone of the Twin Otter aircraft. The measurements include: cloud droplet sizes (2 to 50 µm), concentration and integrated cloud liquid water content. (Instrument team: Bower/Dorsey/Gallagher UoM)
DMT Passive Cavity Aerosol Spectrometer (PCASP-100X) The DMT Passive Cavity Aerosol Spectrometer (PCASP-100X) collects light scattered over angles 35-120o by single particles that pass through the beam generated by a HeNe multi-mode classical passive cavity laser. The scattered light intensity covers more than six orders of magnitude to allow detection and sizing of small aerosol particles. The sample volume is 1 cm3 s-1. The probe is mounted in an under-wing pod. The measurements include: aerosol particle sizes (0.1 to 3.0 µm) and concentration. (Instrument team: Bower/Gallagher/Dorsey, UoM).