NASA - National Aeronautics and Space Administration

SLIT is a high-resolution slit-spectrgraph which is fed by optical fiber attached to window assembly telescope. Its objective is to resolve shock emissions in the near-UV.

The instrument consists of a computer controlled slit-spectrograph which is fed by an optical fiber and a small telescope assembly at the window. A co-aligned camera provides pointing capability, detecting stars to magnitude +7. The camera is an EM CCD Andor DU97 IN, back illuminated UV enhanced CCD, with 1600x400 pixels (16x16 micron) and 25.6 x 6.4 mm image area. The Spectrometer is an Acton Sp300i imaging spectrometer with 300 mm focal length F/D 4.5. The telescope assembly focussing is performed with a 90 degree off-axis parabolic mirror of 50 mm diameter with a focal length of 100mm. The F/D~2 was chosen to meet the numerical aperture of the fibre optics yielding an angle of view of 0.45 degree. A bundle of 50 quartz fibres of 100 µm diameter are chosen. On the telescope side the fibres form a round cross section of 0.8 mm diameter, on the spectrometer side they are oriented in a row which can be used like a slit with a height of 5.6 mm and a width of 100 micron. If sufficient amounts of light are available, a slit can be used in addition to improve the spectral resolution.

The tunable diode laser (TDL) absorption instrument consists of a very high resolution scanning near-infrared diode laser spectrometer. The laser diode is a 3 mW single-mode distributed feedback (DFB) InGaAsP/InP laser that is cooled and temperature stabilized via a Peltier cooler. The laser is scanned in frequency by varying the injection current linearly. The resulting frequency scan covers the entire CH4 R(3) ro-vibrational transition in the 2ν3 overtone band at 1.653 μm.

Because the line strengths are very weak for this overtone transition, the laser beam is multipassed through a custom designed low volume astigmatic Herriott cell yielding a total optical pathlength of 245 m. The transmitted light is detected by a dc-coupled InGaAsP detector and digitized by a custom 20-bit A/D converter. This ADC is synchronized to the 16-bit software generated laser scan waveform running in continuous DMA mode. The laser scans continuously over the methane absorption at a rate of 0.25 - 0.5 KHz and coadds typically 100 scans in a 2 second integration time.

By use of the Beer-Lambert law, the methane number density is calculated from the direct absorption measurements. This calculation is performed by a non-linear least squares Voigt fitting program. The program constraints include the measured cell temperature and pressure in addition to the known absorption line strengths and pressure broadening coefficients associated with the three transitions that make up the R(3) lineshape.

NIRSPEC detects shock emissions in the range 0.96 - 1.67 micron and measures blackbody continuum in the near-Infrared where the blackbody continuum peaks at lower temperatures.

The instrument consists of an InGaAs camera with a 600 l/mm objective grating. The InGaAs camera detects stars of about J-magnitude +2, meteors of about magnitude -1. The co-aligned intensified camera detects stars of magnitude +6.

The miniature Echelle spectrograph provides gigh-resolution Echelle spectroscopy, whereby the spectral range (360 - 900 nm) is folded into shorter segments and projected on a CCD camera for simultaneous exposure.

This instrument consists of a 100 mm f4.5 UV Nikkor lens and Catalina Scientific Corp. "Echellette" Spectrograph with Visible Module or UV Module coupled to a Q-Imaging "Intensified Retiga" blue-enhanced image intensified CCD camera.

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 highest possible spectral resolution.

Provides spectral (and imaging) information at a rate of 1000 frames per second for detection of ablation anomalies, flicker in bowshock emissions, spacecraft rotation, and wake.

The instrument consists of a digital intensified CCD camera capable of 1000 frames per second, equipped with a 600 l/mm objective transmission grating.

The instrument uses two-tone frequency modulation (TTFM) with signal detection at approximately equals 12 MHz. Multiplexing is achieved using a dichroic optical element and a mechanical chopper which blocks each beam alternately. A control program running on a dedicated digital signal processor (DSP) allows the registration of the full absorption line shape each millisecond and simultaneous zero overhead on-line data reduction using a multiple linear regression algorithm. Gas exchange through the compact multireflection cell (2.71 volume, total path 53 m.) takes place in approximately equals 200 ms and thus determines the instrument response time.

GAMS/LAABS is a combination of the Gas and Aerosol Measurement System (GAMS) and the Langley Airborne A-Band Spectrometer (LAABS). The instruments are optically co-aligned and use a common pointing system to track the Sun through an aircraft view port. In the field the instrument provides line-of-sight (LOS) O3, NO2, O4, and water vapor measurements using both a SAGE III-like multiple linear regression algorithm and a full spectrum algorithm. Aerosol may also be derived for ‘enhanced’ conditions including polar stratospheric clouds and optically thin cirrus. Using profile data (1-D/2-D) transformed to GAMS/LAABS LOS geometry, quick-look validation/comparison products for SAGE III, AROTAL, AATS-14, SCIAMACHY, and other instruments will be obtained. The data from GAMS/LAABS will make possible crucial evaluations of SAGE III data processing possible following deployment. These activities include SAGE III etaloning/mirror correction validation, O2 spectroscopy and forward model verification, ozone spectroscopy near the O2 A band and 940-nm water vapor features, evaluation of the relative strength of spectroscopic features (e.g., water vapor features at 600 nm and 940 nm) and altitude registration validation using oxygen measurements.

Instrument Details:

Gas and Aerosol Measurement Sensor (GAMS)

o Solar spectrometer with 1024 channels from ~ 430 to 1030 nm
o Provides measurements of LOS transmission spectra and
differential O3, H2O, O2, O4, and aerosol
o Solar imager to monitor scene homogeneity
o Focus on UV-Vis-Near-IR solar occultation only
o Designed to extend the technique into the troposphere
o Built space flight-like spectrometer, telescope, photon-to-bits
boards, & MCM (detector controller).
o COTS imager to establish imager performance requirements

Langley Airborne A-Band Spectrometer (LAABS)

• High spectral resolution (~0.035 nm) grating spectrometer with > 800
channels from ~759 to 771 nm
• Provides measurements of LOS transmission spectra for evaluation of
SAGE III O2 A-band forward model
• Originally developed to support CALIPSO (formerly PICASSO-CENA)
spaceborne A-band spectrometer
• Designed and fabricated by BATC to provide high spectral resolution
(~0.035 nm) radiance measurements in O2 A-band spectral region
(~765 nm)

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.

The SAFS instruments determine wavelength dependent actinic flux from 280-420 nm. The actinic flux in combination with the absorption cross section and quantum yield molecular data will be used to calculate the photolysis frequencies of multiple photochemically important molecular processes, including O3, NO2, HONO, CH2O, H2O2, CH3OOH, HNO3, PAN, CH3NO3, CH3CH2NO3, and CH3COCH3.

The SAFS measurement is based on a 2p steradian hemisphere hemispherical quartz light collector, a double monochromator, and a low dark current photomultiplier. The monochromator employs dual 2400 G/mm gratings which produce a 1 nm FWHM spectral resolution and very low straylight. The instrument package on the aircraft includes two independent, but time synchronized (IRIG-B) spectroradiometer systems to measure the up- and down-welling fluxes in a 10 second scan time. Summing these produces the spherically integrated actinic flux.