Upendra N. Singh

Validation of temperature measurements from the Halogen Occultation Experiment

The Halogen Occultation Experiment (HALOE) onboard UARS measures profiles of limb path solar attenuation in eight infrared bands. These measurements are used to infer profiles of temperature, gas mixing ratios of seven species, and aerosol extinction at five wavelengths. The objective of this paper is to validate profiles of temperature retrieved from atmospheric transmission measurements in the 2.80-μm CO2 band. Temperatures are retrieved for levels above where aerosol affects the signals (35 km) to altitudes where the signal-to-noise decreases to unity (∽85 km). At altitudes from 45 to 35 km the profile undergoes a gradual transition from retrieved to National Meteorological Center (NMC) temperatures and below 35 km the profile is strictly from the NMC. This validation covers the uncertainty analysis, internal validations, and comparisons with independent measurements. Monte Carlo calculations using all known random and systematic errors determine typical measurement uncertainties of 5 K for altitudes below 80 km. Comparisons of coincident HALOE sunrise and sunset measurements are an indicator of the upper limit of measurement uncertainty. The sunrise-sunset comparisons have random and systematic differences which are less than 10 K for altitudes below 80 km. Comparisons of HALOE to lidar and rocket measurements typically have random differences of ∽5 K for altitudes below 65 km. The mean differences for the correlative comparisons indicate that HALOE temperatures have a cold bias (2 to 5 K) in the upper stratosphere and stratopause.

Validation of UARS Microwave Limb Sounder temperature and pressure measurements

The accuracy and precision of the Upper Atmosphere Research Satellite (UARS) Microwave Limb Sounder (MLS) atmospheric temperature and tangent-point pressure measurements are described. Temperatures and tangent-point pressure (atmospheric pressure at the tangent height of the field of view boresight) are retrieved from a 15-channel 63-GHz radiometer measuring O2 microwave emissions from the stratosphere and mesosphere. The Version 3 data (first public release) contains scientifically useful temperatures from 22 to 0.46 hPa. Accuracy estimates are based on instrument performance, spectroscopic uncertainty and retrieval numerics, and range from 2.1 K at 22 hPa to 4.8 K at 0.46 hPa for temperature and from 200 m (equivalent log pressure) at 10 hPa to 300 m at 0.1 hPa. Temperature accuracy is limited mainly by uncertainty in instrument characterization, and tangent-point pressure accuracy is limited mainly by the accuracy of spectroscopic parameters. Precisions are around 1 K and 100 m. Comparisons are presented among temperatures from MLS, the National Meteorological Center (NMC) stratospheric analysis and lidar stations at Table Mountain, California, Observatory of Haute Provence (OHP), France, and Goddard Spaceflight Center, Maryland. MLS temperatures tend to be 1–2 K lower than NMC and lidar, but MLS is often 5 – 10 K lower than NMC in the winter at high latitudes, especially within the northern hemisphere vortex. Winter MLS and OHP (44°N) lidar temperatures generally agree and tend to be lower than NMC. Problems with Version 3 MLS temperatures and tangent-point pressures are identified, but the high precision of MLS radiances will allow improvements with better algorithms planned for the future.

Raman dial measurements of stratospheric ozone in the presence of volcanic aerosols

Since the eruption of Mt. Pinatubo in June, 1991, measurements of atmospheric species which depend on Rayleigh scattering of radiation, have been severely compromised where the volcanic aerosol cloud exists. For the GSFC stratospheric ozone lidar, this has meant that ozone determination has been impossible below approximately 30 km. The GSFC lidar has been modified to detect Raman scattering from nitrogen molecules from transmitted laser wavelengths. The instrument transmits two laser wavelengths at 308 nm and 351 nm, and detects returns at four wavelengths; 308 nm, 332 nm, 351 nm, and 382 nm. Using this technique in conjunction with the Rayleigh DIAL measurement, ozone profiles have been measured between 15 and 50 km.

Accuracy and precision of cryogenic limb array etalon spectrometer (CLAES) temperature retrievals

The Cryogenic Limb Array Etalon Spectrometer (CLAES) measured emission from the 792 cm−1 Q branch of CO2, from which temperature distributions in the stratosphere and low mesosphere were derived. Here we briefly review the measurement technique, concentrating on aspects that affect the temperature determination. Comparison of many pairs of retrievals at the same location (near 32°N or 32°S) measured on sequential orbits (time separation of 96 min) shows a precision ranging from approximately 0.8 K at 68 mbar to about 3.5 K at 0.2 mbar, which agrees with simulations incorporating random noise and short-period spacecraft motions. Comparisons of globally analyzed CLAES data with National Meteorological Center (NMC) and U.K. Meteorological Office (UKMO) analyses show general agreement, with CLAES tending to be cooler by about 2 K, except in the tropics and high-latitude winter conditions. This is supported by comparisons with individual radiosondes and several lidars that indicate that the agreement is within 2 K throughout the profile (except for a narrow layer around 3 mbar). An error analysis also indicates that systematic errors should be roughly 2 K, independent of altitude. The systematic differences at low latitudes appear to be due to tropical waves, which have vertical wavelengths too short to be seen by the TIROS Operational Vertical Sounder (TOVS) instruments. There are no correlative rocketsondes or lidars to help resolve the reasons for the high-latitude differences. Comparisons with other Upper Atmosphere Research Satellite (UARS) data should shed additional light on this question.

Stratospheric temperature measurements by two collocated NDSC lidars during UARS validation campaign

The NASA Goddard Space Flight Center (GSFC) mobile lidar system was deployed at the Observatoire de Haute Provence (OHP), during an Upper Atmosphere Research Satellite (UARS)/Network for Detection of Stratospheric Change (NDSC) correlative measurement campaign (July–August 1992). The objective of this campaign was twofold: to intercompare two independent lidars and to provide ground-based UARS correlative ozone and temperature validation measurements. This paper, for the first time, presents a coincident temperature intercomparison between two independently operating temperature lidar systems of similar capabilities. Systems and retrieval algorithms have been described and discussed in terms of error sources. The comparison of the two analyses have shown very similar results up to the upper mesosphere. The statistical mean differences of 0.5 K in the stratosphere and about 2 K in the mesosphere suggests insignificant bias throughout except below 35 km, where one of the data sets is contaminated by the volcanic aerosols from the eruption of Mount Pinatubo. Profiles of the root-mean-square (RMS) of the differences are in good agreement with random error estimates, except around 35–40 km where RMS is larger. These measurements can be used as the ground reference for UARS temperature validation. However, the spatial-temporal coincidence between satellite and lidar needs to be carefully considered for meaningful validation.

Correlation of ozone loss with the presence of volcanic aerosols

Statistically significant reductions of ozone compared to a climatological profile have been measured above the Observatoire de Haute Provence (OHP) in Southern France (43.9 deg N, 5.7 deg E) during the months of July and August, 1992. Lidar profiles of ozone, temperature and aerosols were recorded on 25 separate nights during that time. The change in the ozone profile is correlated with the presence of volcanic aerosols from the eruption of Mt. Pinatubo. The total ozone loss amounts to approximately a 10% reduction in the total ozone column over OHP.

Multi-wavelength profiles of aerosol backscatter over Lauder, New Zealand, 24 November 1992

Simultaneous profiles of aerosol backscatter ratio were measured over Lauder, New Zealand (45°S, 170°E) on the night of November 24, 1992. Instrumentation comprised two complementary lidar systems and a backscattersonde, to give measurements at wavelengths 351, 490, 532 and 940 nm. The data from the lidars and the backscattersonde were self-consistent, enabling the wavelength dependence of aerosol backscatter to be determined as a function of altitude. This wavelength-dependence is a useful parameter in radiative transfer calculations. In the stratosphere, the average wavelength exponent between 351 and 940 nm was −1.23±0.1, which was in good agreement with values derived from measured physical properties of aerosols.

Lidar temperature measurements during the Tropical Ozone Transport Experiment (TOTE)/Vortex Ozone Transport Experiment (VOTE) mission

Temperature profiles were acquired on the Tropical Ozone Transport Experiment (TOTE) and Vortex Ozone Transport Experiment (VOTE) flights by the Goddard Airborne Raman Lidar. The objective was to compare the temperature product from this new instrument with those generated by the Jet Propulsion Laboratorys Microwave Temperature Profiler and Goddard Space Flight Centers ground-based Stratospheric Ozone Lidar. Simultaneous measurements were made between the Airborne Raman Lidar and O3 lidar on three dates; average temperatures differences varied from ∼0.5 K-5 K over the 16–24 km altitude region. Comparisons between the Microwave Temperature Profiler and Airborne Raman Lidar for all flights (17) during TOTE/VOTE were performed over the same altitude region. The average temperature difference, Airborne Raman Lidar minus Microwave Temperature Profiler, was +2.3 K. In comparing temperatures between the Airborne Raman Lidar and Goddards Data Assimilation Model, the ARL showed small scale structures not evident in those of the model for altitudes between ∼16 and 43 km.

High Repetition Rate and Frequency Stabilized Ho:YLF Laser for CO2 Differential Absorption Lidar

High repetition rate operation of an injection seeded Ho:YLF laser has been demonstrated. For 1 kHz operation, the output pulse energy reaches 5.8mJ and the optical-to-optical efficiency is 39% when the pump power is 14.5W.

High Energy Totally Conductive Cooled, Diode Pumped, 2µm Laser

This paper describes the design and performance a totally conductive cooled, space-qualify-able high-energy 2-µm laser. Over 230mJ normal mode energy and 107mJ of Q-switched energy has been achieved.