A high-resolution Fabry-Perot spectrometer has been used at Fritz Peak Observatory (39.9 degreeN, 105.5 degreeW) to determine the nighttime thermospheric temperature and winds from November 1973 through February 1975. The thermospheric temperature and winds at a height near the F/sub 2/ peak are determined from the Doppler broadening and shift, respectively, of the atomic oxygen line emission at 15867.852 K (6300.308 A). The experimentally derived temperatures and winds during geomagnetically quiet conditions are compared with a three-dimensional semiempirical model of the neutral thermosphere. This model in turn uses global empirical models of neutral temperature, composition, and electron density to determine the pressure forces and ion drag which generate and modify the wind fields. The large-scale details of measured and calculated nighttime meridional wind components are in general agreement, showing maximum equatorward winds during the summer months. Measured and calculated zonal winds agree for the equinoctial and winter months; however, the measured nighttime zonal winds are westward during summer months in constrast to model calculations that indicate a midnight eastward to westward transition. The measurements also indicate that both the temperature and the equatorward component of the meridional wind measured north of the observing station are greater than those measured southmore » of the station. These positive latitudinal temperature and wind gradients are greatest during the summer months. (AIP)« less

Direct measurements of nighttime thermospheric winds and temperatures, 1. Seasonal variations during geomagnetic quiet periods

Reliable Nd:YAG laser technology and currently available optical sensors are presently used to reevaluate the performance of an incoherent Doppler lidar system operating at 354.7 nm. This system makes a more efficient use of output laser power than heretofore possible through a matching of the usable and detectable field of view of the Fabry-Perot interferometer receiver with that of the transmitter. Major advantages accrue to this system from the lower output power requirement, which is a primary cost driver for the prospective Spaceborne Doppler Wind Lidar.

Doppler lidar atmospheric wind sensor: reevaluation of a 355-nm incoherent Doppler lidar.

We present a refractive index (RI) sensor based on a fiber Mach–Zehnder interferometer (MZI) formed by two cascaded special long-period fiber gratings (LPFGs) with rotary refractive index modulation (RLPFGs), in which the coupling occurred between the guided mode and the high-order asymmetric cladding mode. The experimental results show that the RI sensitivity of a refractometer with an interaction length of 40 mm is up to 58.8 nm/RI in the range of 1.3344 to 1.3637, which is 3.5 times higher than that of an MZI formed by two normal LPFGs. The temperature sensitivity for the same parameters of an RLPFG-MZI is about 0.03 nm/°C. Such a kind of high-sensitivity, easy-to-fabricate and simple-structure interferometer may find applications in the chemical or biochemical sensing fields.

Highly sensitive refractive index sensor based on two cascaded special long-period fiber gratings with rotary refractive index modulation

A simple analytic model is developed for the shot-noise-limited measurement precision of Doppler wind lidars based on the fringe imaging technique by use of either molecular or aerosol atmospheric backscatter. The model leads to etalon design parameters for an instrument optimized for precision. The ultimate measurement precision possible is two to four times the limit for a perfect, lossless receiver. The corresponding result for the double-edge Doppler analyzer was a ratio of 2.5, showing that the two methods are little different in this respect. For aerosol backscatter instruments, the wind speed dynamic range of the fringe imager is substantially greater than that for the edge detector. The etalon aperture needed to meet system etendue requirements is derived and shown to be approximately half that of each of the two etalons required by the double-edge technique. A comparison with more detailed modeling of fringe imaging Doppler-shift analyzers shows good agreement for the Rayleigh model and fair for the aerosol version, confirming the validity of this simpler technique for analyzer design and performance prediction.

Modeling of direct detection Doppler wind lidar. II. The fringe imaging technique

The theoretical performance of a Mach–Zehnder interferometer used
as a spectral analyzer for wind-speed measurement by direct-detection
Doppler lidar is presented. The interferometer is optimized for
measurement of wind velocity from the signal backscattered by the
molecules. Two arrangements are proposed, involving two detection
channels (DMZ) or four detection channels (QMZ). Using the
assumption of a pure molecular signal with a Gaussian spectral profile,
we derive an analytic expression for the standard deviation of the
measurement error for each arrangement. They are then compared with
the ideal spectral analyzer (ISA) and with the double-edge
Fabry–Perot (DFP) in the case of a shot-noise-limited
signal. The DMZ measurement error is shown to be only 1.65 times
that of the ISA and is 1.4 times lower than that given by the
DFP. The QMZ arrangement provides a measurement that is insensitive
to the aerosol scattering contribution but gives a measurement error
that is 1.4 times higher than that of the DMZ.

Mach-zehnder interferometer as a spectral analyzer for molecular Doppler wind lidar.

The sampling theorem for deterministic functions is used to locate the center of
					gravity of a spectral line obtained by photon counting with a multichannel
					spectrometer. The sampling step and the width of the channels have been
					evaluated to locate the line with maximum accuracy. Our analysis and
					experimental results give the requirements needed of a photon counting
					multichannel Fabry-Perot spectrometer to improve the accuracy of measurement of
					the spectral interval between two lines.

Méthode d’echantillonnage des fonctionsdéterministes en spectroscopie: application à unspectromètre multicanal par comptage photonique

The sampling theorem for deterministic functions is used to locate the center of gravity of a spectral line obtained by photon counting with a multichannel spectrometer. The sampling step and the width of the channels have been evaluated to locate the line with maximum accuracy. Our analysis and experimental results give the requirements needed of a photon counting multichannel Fabry-Perot spectrometer to improve the accuracy of measurement of the spectral interval between two lines.

Méthode d'echantillonnage des fonctions déterministes en spectroscopie: application à un spectromètre multicanal par comptage photonique.

This paper describes the principles, realization, and characteristics of a refractometer used as a reference for measuring the scanning of a high resolution, photoelectric Fabry-Perot spectrometer. The precision of the measurements on this refractometer is approximately one order of magnitude greater than that obtainable with other instruments.

Jean-Pierre Saint-Dizier

Papers

Méthode d’echantillonnage des fonctionsdéterministes en spectroscopie: application à unspectromètre multicanal par comptage photonique

Méthode d'echantillonnage des fonctions déterministes en spectroscopie: application à un spectromètre multicanal par comptage photonique.

Refractometer associated with the fabry-perot spectrometer.