Twin Otter[VP-FAZ]

Four aircraft of the DHC 6 300 series with STOL capabilities. They can operate from paved and unpaved surfaces. All four can undertake polar logistics support including to sea-ice camps. They can be equipped with wheel skis and have extended range tanks fitted. Two aircraft are modified to support airborne and remote sensing applications.

The type of science supported

The aircraft have supported research monitoring and recording interactions between the Earth’s crust, ice- and snow-covered areas, oceans and the atmosphere. This is both from a logistics perspective in deploying instruments and field camps but also as airborne research platforms

• Mapping of the Earth’s magnetic and gravity field, ice thickness & structure, sea ice thickness, snow thickness on sea ice, surface morphology/altimetry
• Measuring in-situ and remotely aerosols and trace gases
• Measuring temperatures, humidity, wind distribution
• Radiation measurements
• Optical remote sensing

Instrumentation for Atmospheric Research:

Total Temperature

Goodrich Rosemount Probes mounted on the nose. A non-de-iced model 102E4AL and a de-iced model 102AU1AG logged at 0.7Hz.

Altitude and Position

GPS NMEA and one pulse per second (1pps) is distributed to all systems to provide synchronisation of all the data and formation of coherent data sets.

Air Speed

Static and dynamic pressure from the aircraft static ports and heated pitot tube, 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 10Hz.

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 2kHz.

Cameras

Two Sony DV-tape cameras can be used. One downwards-looking mounted in the camera hatch, one forward-looking mounted in the cockpit. A Canon EOS7D with 15mm lens can be triggered to take 18MP images at up to 1 frame/sec.

Laser Scanner

A Riegl Q240 80 degree laser scanner has been used for mapping sea ice.

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

A 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. Three-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

Around 5m position accuracy 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.

GPS Attitude and Reference System

A JAVAD AT4 4-antenna GPS system records heading, pitch and roll at 20Hz and velocites at 10Hz. Antennas are permanently fitted to each wingtip and fore and aft of the fuselage.

Inertial Attitude and Heading Systems

Aircraft attitudes and rate of change are recorded from the aircraft avionics Litef AHRS system. This is converted from ARINC format at 64Hz. There is also an OXTS Inertial+ GPS linked INU available which stores data internally operating at 100Hz.

Wing Hardpoints

Both wings have hardpoints, zivko carbon fibre pylons and cabling to accept PMS footprint instruments.

Cloud Probe

An under-wing pylon mounted Droplet Measurement Technologies CAPS Probe comprises of a 2D imaging probe (25μm-1550μm), aerosol spectrometer (0.5μm-50μm) and liquid water content probe (0.01-3.0g/m3). The probe has a dedicated logging PC and comprehensive instrument de-icing heaters. An under-nose mount for a DMT CDP instrument has also been fitted.

Closed Path water vapour and CO2 sensor

A LICOR LI-7000 closed path infra-red gas analyser is fitted. Sampling is from a Rosemount inlet and readings are triggered at 50Hz.

Aerosol Inlet

A Brechtel Model 1200 Isokinetic Inlet is fitted. >95% efficient for 0.01μm to 6μm.

Condensation Particle Counter

A TSI 3772 CPC is available.

Aerosol Spectrometer

A Grimm model 1.109 portable aerosol spectrometer. 31 channels 0.25μm to 32μm.

Central Logging System

All instruments apart from the CAPS probe 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. CAPS has a dedicated computer. Dual KVM switches allow both the rear operators screen and the cockpit display to switch to either PC.

ASIRAS

ASIRAS is an airborne SAR-altimeter instrument owned by ESA.

ASIRAS is essentially a Ku-band altimeter but with a high pulse repetition frequency such that it is phase sensitive and pulse-coherent. The carrier frequency of the radar is 13.5 GHz and the bandwidth is 1 GHz. It returns information on surface snow including over sea ice.