Determining tunable diode laser spectrometer performance through measurement of N(2)0 line intensities and widths at 7.8 microm.

The N(2)O R(8) doublet of the 11(1)0-01(1)0 band at 7.8 microm was measured by a tunable diode laser spectrometer designed and assembled at Perkin-Elmer. The spectra were digitized and least-squares fitted to Voigt line profiles to yield N(2)O line parameters and a quantitative measure of instrument performance. Scans at various pressures produced consistent spectral line values: S(0) = (0.1746 +/- 0.0043)cm(-2)/atm at 300 K, alpha(L)(N(2)O - N(2)O) = (0.1066 +/- 0.0041)cm(-1)/atm,alpha(D) = (1.194 +/- 0.018) x 10(-3) cm(-1), andalpha(L)(N(2)O - N(2)) = (0.0870 +/- 0.0015)cm(-1)atm. A spectrum with several levels of synthetic noise added was used to verify the fitting algorithm's stability. The spectrometer was shown to possess an excellent SNR (e.g., 900:1) and wave number precision (

Quantitative remote measurements of pollutants from stationary sources using Raman lidar.

The several advantages of Raman lidar for remote measurements of stationary source emissions were quantitatively evaluated using a calibration tank at a distance of 300 m at night. Measurements of ~10(3)-ppm SO(2) with a 12% accuracy were demonstrated in an observation time of 15 min using a 1.5-J ruby laser at 30 pulses/ min, 6-m range resolution, interference filters, photon counting detection, and a 20-cm receiver. Measurement accuracy was checked by measuring known concentrations of SO(2) in the tank, by tuning the interference filters through the SO(2) Raman line, and by varying the CO(2) concentration to very high levels during the SO(2) measurements. Evaluation of the seriousness of induced fluorescence from plume aerosols failed due to the inability to simulate the plume aerosols.

The Lunar Laser Ranging Experiment: Accurate ranges have given a large improvement in the lunar orbit and new selenophysical information.

The lunar ranging measurements now being made at the McDonald Observatory have an accuracy of 1 nsec in round-trip travel time. This corresponds to 15 cm in the one-way distance. The use of lasers with pulse-lengths of less than 1 nsec is expected to give an accuracy of 2 to 3 cm in the next few years. A new station is under construction in Hawaii, and additional stations in other countries are either in operation or under development. It is hoped that these stations will form the basis for a worldwide network to determine polar motion and earth rotation on a regular basis, and will assist in providing information about movement of the tectonic plates making up the earth's surface. Several mobile lunar ranging stations with telescopes having diameters of 1.0 m or less could, in the future, greatly extend the information obtainable about motions within and between the tectonic plates. The data obtained so far by the McDonald Observatory have been used to generate a new lunar ephemeris based on direct numerical integration of the equations of motion for the moon and planets. With this ephemeris, the range to the three Apollo retro-reflectors can be fit to an accuracy of 5 m by adjusting the differences in moments of inertia of the moon about its principal axes, the selenocentric coordinates of the reflectors, and the McDonald longitude. The accuracy of fitting the results is limited currently by errors of the order of an arc second in the angular orientation of the moon, as derived from the best available theory of how the moon rotates in response to the torques acting on it. Both a new calculation of the moon's orientation as a function of time based on direct numerical integration of the torque equations and a new analytic theory of the moon's orientation are expected to be available soon, and to improve considerably the accuracy of fitting the data. The accuracy already achieved routinely in lunar laser ranging represents a hundredfold improvement over any previously available knowledge of the distance to points on the lunar surface. Already, extremely complex structure has been observed in the lunar rotation and significant improvement has been achieved in our knowledge of lunar orbit. The selenocentric coordinates of the retroreflectors give improved reference points for use in lunar mapping, and new information on the lunar mass distribution has been obtained. Beyond the applications discussed in this article, however, the history of science shows many cases of previously unknown, phenomena discovered as a consequence of major improvements in the accuracy of measurements. It will be interesting to see whether this once again proves the case as we acquire an extended series of lunar distance observations with decimetric and then centimetric accuracy.

Direct Measurement of the Quantum Counting Efficiency of RCA C31000E/F Photomultipliers at 6328 A.

Direct measurement of the total quantum counting efficiency of the RCA C31000E/F shows that it is about 25 +/- 22% lower than the photocathode quantum efficiency in optimized commercial base units. Measurements with an EMI 9558 give similar results and with an Amperex 56TVP give similar although more erratic results due to its higher sensitivity to magnetic fields. The measurement techniques and conditions are described in detail. Diagnostic studies such as the question of dependence of counting efficiency on signal or background count rate are also presented.

Laser ranging retro-reflector: continuing measurements and expected results.

After successful acquisition in August of reflected ruby laser pulses from the Apollo 11 laser ranging retro-reflector (LRRR) with the telescopes at the Lick and McDonald observatories, repeated measurements of the round-trip travel time of light have been made from the McDonald Observatory in September with an equivalent range precision of +/-2.5 meters. These acquisition period observations demonstrated the performance of the LRRR through lunar night and during sunlit conditions on the moon. Instrumentation activated at the McDonald Observatory in October has yielded a precision of +/-0.3 meter, and improvement to +/-0.15 meter is expected shortly. Continued monitoring of the changes in the earth-moon distance as measured by the round-trip travel time of light from suitably distributed earth stations is expected to contribute to our knowledge of the earth-moon system.

Apollo 11 Laser Ranging Retro-Reflector: Initial Measurements from the McDonald Observatory.

Acquisition measurements of the round-trip travel time of light, from the McDonald Observatory to the Laser Ranging Retro-Reflector deployed on the moon by the Apollo 11 astronauts, were made on 20 August and on 3, 4, and 22 September 1969. The uncertainty in the round-trip travel time was +/- 15 nanoseconds, with the pulsed ruby laser and timing system used for the acquisition. The uncertainty in later measurements of a planned long-term sequence from this observatory is expected to be an order of magnitude smaller. The successful performance of the retro-reflector at several angles of solar illumination, as well as during and after a lunar night, confirms the prediction of thermal design analyses.