Twin Otter - CIRPAS
CIRPAS Twin Otter
NPS Twin Otter
Associated content: 

Twin Otter - CIRPAS - NPS

Naval Postgraduate School CIRPAS Twin Otter

A Twin Otter research aircraft has been operated by the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) at the Naval Postgraduate School in Monterey, CA  since 1998.  The aircraft supports atmospheric and oceanographic research for Office of Naval Research, National Science Foundation, Department of Energy, National Oceanographic and Atmospheric Administration, NASA, and others.  The airplane is instrumented to measure the meteorological state variables, flight path and platform attitude, turbulence, aerosol particle concentration and size spectra, cloud and precipitation drop concentration and size spectra, light scatter and absorption coefficients and sea surface temperature.  Ample room is in the cabin for rack-mountable guest instruments.  Well characterized aerosol community inlet provides air samples into the cabin.  Nadir and zenith ports provide up and down view for radiometers, sunphotometers and imaging instruments.  Satellite communication system permits flight following from the ground and viewing of data in real time, as well as chat-room communication between flight scientist and science team on ground. 

Naval Postgraduate School Center for Interdisciplinary Remotely Piloted Aircraft Studies
Conventional fixed wing, twin turboprop
5 hours (payload and weather dependent)
Useful Payload: 
1 500 lbs
Gross Take-off Weight: 
13 500 lbs
Onboard Operators: 
Max Altitude: 
Air Speed: 
100 knots
300 Nmi
200 A, 28VDC (up to 4KVA, 115VAC)
Point(s) of Contact: 

Roy Woods

Work: (831) 384-2776 ext. 12
(831) 241-4800
Co-Authored Publications: 
Note: Only publications that have been uploaded to the ESD Publications database are listed here.

Haflidi Jonsson

(831) 384-2776 ext. 11
(831) 241-4806
Co-Authored Publications: 
Note: Only publications that have been uploaded to the ESD Publications database are listed here.

Solar Spectral Flux Radiometer

In early 2000, the Ames Atmospheric Radiation Group completed the design and development of an all new Solar Spectral Flux Radiometer (SSFR). The SSFR is used to measure solar spectral irradiance at moderate resolution to determine the radiative effect of clouds, aerosols, and gases on climate, and also to infer the physical properties of aerosols and clouds. Additionally, the SSFR was used to acquire water vapor spectra using the Ames 25-meter base-path multiple-reflection absorption cell in a laboratory experiment. The Solar Spectral Flux Radiometer is a moderate resolution flux (irradiance) spectrometer with 8-12 nm spectral resolution, simultaneous zenith and nadir viewing. It has a radiometric accuracy of 3% and a precision of 0.5%. The instrument is calibrated before and after every experiment, using a NIST-traceable lamp. During field experiments, the stability of the calibration is monitored before and after each flight using portable field calibrators. Each SSFR consists of 2 light collectors, which are either fix-mounted to the aircraft fuselage, or on a stabilizing platform which counteracts the movements of the aircraft. Through fiber optic cables, the light collectors are connected to 2 identical pairs of spectrometers, which cover the wavelength range from (a) 350 nm-1000 nm (Zeiss grating spectrometer with Silicon linear diode array) and (b) 950 nm - 2150 nm (Zeiss grating spectrometer with InGaAs linear diode array). Each spectrometer pair covers about 95% of the incoming solar incident irradiance spectrum.

Instrument Type: 
Point(s) of Contact: 

Diode Laser Hygrometer

The DLH has been successfully flown during many previous field campaigns on several aircraft, most recently ACTIVATE (Falcon); FIREX-AQ, ATom, KORUS-AQ, and SEAC4RS (DC-8); POSIDON (WB-57); CARAFE (Sherpa); CAMP2Ex and DISCOVER-AQ (P-3); and ATTREX (Global Hawk). This sensor measures water vapor (H2O(v)) via absorption by one of three strong, isolated spectral lines near 1.4 μm and is comprised of a compact laser transceiver and a sheet of high grade retroflecting road sign material to form the optical path. Optical sampling geometry is aircraft-dependent, as each DLH instrument is custom-built to conform to aircraft geometric constraints. Using differential absorption detection techniques, H2O(v) is sensed along the external path negating any potential wall or inlet effects inherent in extractive sampling techniques. A laser power normalization scheme enables the sensor to accurately measure water vapor even when flying through clouds. An algorithm calculates H2O(v) concentration based on the differential absorption signal magnitude, ambient pressure, and temperature, and spectroscopic parameters found in the literature and/or measured in the laboratory. Preliminary water vapor mixing ratio and derived relative humidities are provided in real-time to investigators.

Instrument Type: 
Point(s) of Contact: 


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