Synonyms: 
DC8
DC-8
NASA DC8
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Fourier Transform Infrared Spectrometer

The absorption of infrared solar radiation along a slant path to the sun is recorded from 2 to 15 micrometers. Six spectral filters are used to cover the region from 2-15 microns. An interferogram is recorded in about 10 seconds. Interferograms are transformed to produce spectra. Column amounts are retrieved by fitting the observed spectra using the non-linear least squares fitting code SFIT2 that employs an Optimal Estimation retrieval algorithm.

The major chlorine reservoirs (HCl and ClONO2), the important nitrogen-containing gases in the stratosphere (N2O, NO, NO2, and HNO3), stratospheric and tropospheric tracers (HF, CH4, C2H6, H2O, CO2), a major source CFC (CF2Cl2) and ozone may be routinely retrieved.

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Langley In Situ Fast-Response Ozone Measurements

• Technique: Chemluminescent reaction of ozone with nitric oxide
• Dynamic Range: 0.6 - 1600 ppb
• Accuracy: 5% or 2 ppb
• Precision: 2% or 0.6 ppb
• Response: 2-3 Hz; recorded at 6 Hz, reported at 1 Hz, faster data on request
• Spatial Resolution: <10 m vertical (aircraft spiral), 200 m horizontal (at 400 kts)

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Fabry-Perot Interferometer

A Fabry-Perot interferometer is constructed of two very flat, partially reflecting mirrors held parallel to one another at a fixed distance. Interference occurs among the multiple reflections leading to the condition that wavelengths that exactly divide the spacing between the mirrors by an integer are transmitted very efficiently and all other wavelengths are reflected. Thus if the plates are held fixed at a separation of 10 μm, then radiation at 10, 5, 3.333, … μm will be transmitted. Note that these wavelengths are equally spaced in energy according to the relationship E=hc/l, where l is the wavelength of the light and h and c are Planck’s constant and the speed of light, respectively. This particular FPI technique makes use of these multiple passbands to increase the measurement signal and the resulting signal to noise ratio.

A Fabry-Perot can be tuned to transmit different wavelengths by changing the (optical) spacing between the mirrors. This is commonly done by employing piezo-electric transducers to translate the mirrors by very small distances, while maintaining the very precise parallelism between them. Fixed gap Fabry-Perots can be tuned by tilting, which changes the effective path length between the plates; by using the thermal expansion and contraction of the spacers between the mirrors; and by changing the composition or pressure of the gas that fills the space between the plates, which alters the index of refraction thereby changing the optical separation. Finally, Fabry-Perots can be constructed using a solid substrate of fused silica or optical quality glass onto which reflective coatings are deposited. These devices can be angle tuned or temperature tuned.

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Dropsondes - DC-8

DC-8 dropsondes measure the vertical profile of atmospheric temperature, pressure, relative humidity, and wind speed and direction as the sonde falls from altitude to ocean surface.

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Ames Digital Imager

The Ames digital imager is a cooled large format NikonTM1 D70 digital camera with a 70-300mm f5.6 Nikon lens. It is used hand-held behind a passenger window with exposure times 1/1000s. The camera uses a SONYTM ICX413AQ CCD detector with image format 3040 x 2014 pixels of size 7.8 microns. It measures total radiative output of the sample return capsule along its trajectory.

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Cooled CCD Slit-less Spectrograph

ASTRO utilizes slit-less spectroscopy with transmission grating, a long focal length lens, and a cooled CCD camera detector.

This instrument consists of a Richardson Grating Laboratory 11 x 11 cm plane transmission grating (35-54-20-660), an AF-S Nikkor f2.8/300 mm Nikon 300D IF-ED lens, and a two-stage thermoelectrically cooled back-illuminated 1024 x 1024 pixel Pixelvision CCD camera. An optional order separation filter.

Scientific objective: Spectral resolution of shock layer radiation. Resolve spectral lines of air plasma emissions at optical wavelengths for the measurement of excitation temperatures. Provide high spectral resolution and absolute calibration at high dynamic range. Limitation: only one measurement made in a brief time interval during the point of peak brightness.

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CN - Hawaii

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Automatic Meteor Tracker with Imager and Slit Spectrograph

The AIM-IT instrument (Meteor Tracker) was developed for rapid pointing and meteor tracking. Its purpose is to image bright meteors in high resolution, searching for jets and other plasma ejections. During the 2001 Leonids, the instrument carried a light collection lens with a fiber optic connection to a spectrograph.

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Airborne Submillimeter Radiometer

The ASUR (Airborne SUbmillimeter Radiometer) is an airborne radiometer measuring the thermal emission of trace gases in the stratosphere (in an altitude range between 15 and 50 km). The instrument detects the radiation in a frequency range between 604.3 and 662.3 GHz. This corresponds to wavelengths of about 0.45-0.5 mm. In this frequency range a major part of the radiation is absorbed by atmospheric water vapor. As most of the water vapor is found in the troposphere (in the Arctic up to 8 km, in the tropics up to 16 km altitude) the instrument is operated on board of an aircraft flying at an altitude of 10-12 km, such that a major part of the water vapor absorption is avoided. Using appropriate inversion techniques vertical profiles from 15 to over 50 km altitude can be retrieved with a vertical resolution of typically 6 km and 12 km in the lower and upper stratosphere, respectively.

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Airborne Laser Terrain Mapper Experiment

Detailed topographic maps of very high accuracy are produced by airborne laser altimeter terrain mapping. The unique capabilities of this new technique yield more comprehensive and precise topographic information than traditional methods. Airborne laser altimeter data can be used to accurately measure the topography of the ground, even where overlying vegetation is quite dense. The data can also be used to determine the height and density of the overlying vegetation, and to characterize the location, shape, and height of buildings and other manmade structures.

The method relies on measuring the distance from an airplane, or helicopter, to the Earth’s surface by precisely timing the round-trip travel time of a brief pulse of laser light. The travel-time is measured from the time the laser pulse is fired to the time laser light is reflected back from the surface. The reflected laser light is received using a small telescope that focuses any collected laser light onto a detector. The travel-time is converted to distance from the plane to the surface based on the speed of light. Typically a laser transmitter is used that produces a near-infrared laser pulse that is invisible to humans. The laser light reaching the ground surface is completely safe. It can not cause any eye damage to a person who might be looking up at the plane as it flies overhead.

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