William E. Sharp

A VALIDATION STUDY OF THE ROBERTSON-BERGER METER

Abstract— An evaluation of the Robertson‐Berger meter was done in order to address the question of whether instrumental and calibration factors can cause what might be interpreted as a change in the ground level solar ultraviolet‐B (UV‐B) flux. The evaluation consisted of reviewing information about the instrumentation and components in the published literature, a review of the records and procedures in both operations and calibrations, and examination of two instruments including temperature tests of them. It is shown that the instrument is basically stable and that the calibration procedures did not support data drift. There is a slight dependance of the two instruments upon temperature, 0.3°C/y and 0.6°C/y, which is not sufficient to lead to the reported UV‐B trends of the order of 0.7 %/y. There is negligible temperature drift in the control electronics.

A comparison of measurements of the oxygen nightglow and atomic oxygen in the lower thermosphere

Abstract We have investigated the relationship between the oxygen nightglow and the atomic oxygen density in the lower thermosphere. This was done using data from two sounding rocket experiments conducted over White Sands Missile Range (32°N, 106°W). The first flight was launched on 2 November 1978 while the second was launched on 7 December 1981. Both flights contained resonance lamps to measure the atomic oxygen density. The peak density in both cases was near 1.9 × 1011 cm−3. In addition, the 1978 flight contained a photometer to measure the 5577 A green line while the 1981 flight contained photometers to measure the green line, the u.v. nightglow, and the 7620 A (0,0) atmospheric band. We have used empirical models of these airglow features to compare with the O density measurements. In the case of the atmospheric band, excellent agreement is seen concerning the shape of the atomic oxygen profile, while some discrepancies were seen with the Herzberg band and the green line. In all cases, the absolute value of our peak O density appeared to be about 2.5 times lower, for a given airglow intensity, than previous measurements.

On the inversion of O+(²D-²P) 7320 Å twilight airglow observations: A method for recovering both the ionization frequency and the thermospheric oxygen atom densities

In this paper we demonstrate that it is possible to invert twilight observations of the O+(²D -²P)-7320 A airglow emission to obtain information about both the thermospheric atomic oxygen densities and the unattenuated O+(²P) ionization frequency. The efficacy of the proposed approach, which relies upon making twilight observations in more than one viewing direction, is illustrated using a synthetic data set and an inversion algorithm based on a simple photochemical model. The results of this study show that day-to-day variations in the thermospheric oxygen atom densities may be monitored from the ground without requiring complementary measurements of the solar EUV flux. The study also shows that twilight observations may be used to monitor variations in the solar flux components that are responsible for O+(²P) production and EUV heating of the upper thermosphere.

Upper limits to (O) in the lower thermosphere from airglow

A method for estimating the upper limit to oxygen atom density in the lower thermosphere is presented. The method is based on an analytical equation for the energy density of recombination process, and the radiation of O2 atoms at excited levels. As an example of the method, upper limits of oxygen atom density are estimated for the CIRA (O2) reference atmosphere of 1972. The estimates are given in a table.

A method for the retrieval of atomic oxygen density and temperature profiles from ground-based measurements of the O+(²D - ²P) 7320-Å twilight airglow

This paper describes a technique for the retrieval of altitude profiles of the atomic oxygen concentration (n = [O]) and temperature (T) from ground-based measurements of the O+(²D - ²P) doublet at 7320 and 7330 A in the twilight airglow. The technique is based on previously demonstrated knowledge that at solar zenith angles (SZA) characteristic of twilight conditions, the upper state of the 7320-A doublet transition is produced by photoionization and photoelectron impact ionization of atomic oxygen and lost mainly by radiative decay, thereby providing a sensitive dependence on [O]. We apply inverse problem theory to retrieve the exospheric temperature (T∞), the atomic oxygen concentration at 120 km (n120), the temperature at 120 km (T120) and the temperature profile shape factor (S) using a Bates-Walker representation of n given approximately by n = (n120T120/T) exp[−z] where T = T∞ - (T∞ - T120)exp[−S(h - h120)], z is the reduced height, and h is the altitude. The algorithm is tested and theoretically verified using synthetic data sets where random errors of measurements are characterized by Poisson noise due primarily to sky background. In the tests that we report here the solar EUV flux is specified. In a separate paper we will report how the solar EUV ionization rate can be independently derived from various twilight emissions. By comparing retrieved with known input values, it is demonstrated that for the altitude range 200 to 500 km the atomic oxygen concentration [O] can be retrieved with relative errors ≃15% and systematic errors of about 25% if the solar EUV is given. Sensitivity of the results to noise, sample size (degrees of freedom), and absolute calibration are quantitatively evaluated. In addition, to demonstrate the validity of the technique experimentally, we utilized the Atmosphere Explorer E (AE-E) in situ measurements of the solar EUV flux and [O], with the latter taken when perigee was over Arecibo on an occasion when the observatory airglow spectrometer was simultaneously measuring the 7320-A emission from the ground during twilight. The results show excellent agreement with the measured [O] values which were ∼ 50% lower than the mass spectrometer incoherent scatter (MSIS-86) model values at ∼ 300 km on that day, thereby demonstrating the value of the method for monitoring day-to-day variations in [O] and the temperature.

Mesospheric temperature inferred from daytime observation of the O2 atmospheric (0, 0) band system

A rocket-borne Ebert-Fastie spectrometer was used to measure the dayglow O2(b¹Σg+) atmospheric (0,0) band centered at 761.9 nm. The tangent altitude for the observations ranged from 63 to 101 km. Analysis of the (0,0) band observations is presented. The peak intensity of the (0,0) band was 3.7±0.2 megarayleigh at 87 km. The results were compared to a multiple-scattering radiative transfer model that includes a detailed photochemical calculation of the sources and sinks of the O2 excited state. The kinetic temperature was determined by analysis of the rotational development of the O2 (0,0) band. The average temperature between 94 and 101 km was 182±7 K.

A vibrational analysis of the O2 (A3Σ+u) Herzberg I system using rocket data

Abstract An observation of the u.v. nightglow between 2670 and 3040 A was conducted over White Sands Missile Range on 22 October 1984. A 1 4 m spectrometer operating at 3.5 A resolution viewed the Earths limb at tangent heights between 90 and 110 km for 120 s. A total of 41 spectral scans of the nightglow were obtained with the brightest feature being the O2 (A3Σu+−X3Σg−) Herzberg I bands. The data were sorted into two groups, one from the top side of the layer and one containing the emission peak, and compared with synthetic spectra. The deduced O2 (A3Σu+) vibrational distributions indicate that at low altitudes, the higher vibrational levels ( v > 6) were relatively depleted; however, the magnitude of the vibrational shift is much less than that predicted from theories of vibrational relaxation. It is shown that increasing the electronic quenching of O2 (A3Σg+) with respect to the vibrational quenching can reduce the vibrational shift in the model and qualitatively explain the observations; however, several details of the vibrational distribution are not well reproduced.

High-speed CW lidar retrieval using spectral lock-in algorithm

A continuous-wave (CW) NIR carbon-dioxide monitoring system, incorporating Wavelength Modulation Spectroscopy (WMS), has been developed and was tested aboard the Spirit of Goodyear airship platform. The data shows sensitivities nearly identical to previous ground-based tests but with much higher information rates (100Hz). These tests were conducted over regions with varying ground albedo and included path lengths up to 1.5 km. The system utilized commercial-off-the-shelf (COTS) components including telecom laser diodes and amplifiers. Currently, the system is limited by Erbium Doped Fiber Amplifier (EDFA) spectral bandwdith, but the ever-increasing average power of quantum cascade lasers coupled with the development of midwave fiber technology could make this CW-based architecture a viable solution for future airborne sensors in the MWIR region.

The HARP plasma experiment on-board the Phobos 2 spacecraft: Preliminary results

Abstract The HARP differential electrostatic analyzer measured thermal and supra thermal electron and ion fluxes and distributions in the Mars environment. High bit-rate data obtained around the pericenter passage on elliptical orbits early in February 1989 will be highlighted, and correlation with results of other experiments will be discussed. A similarity between the HARP total count rate variations and the spacecraft potential measurements of the Plasma-Wave System experiment is established. The variation of electron energy spectra is discussed in various regions of the solar wind interaction with Mars. Tentative results on electron and ion anisotropy are presented, making use of regular variations of the ratio of count rates of two sensor heads looking in perpendicular directions. Magnetic field data of the MAGMA magnetometer are used for comparison.

N I 8680‐ and 8629‐Å multiplets in the dayglow

The N I 8680- and 8629-A multiplets have been observed in the midlatitude dayglow during moderate-to-high solar activity. A rocket-borne near-infrared spectrometer of 13.4-A resolution recorded spectra between 120 and 219 km. Analysis yielded altitude profiles of emissions including the N2 first positive (1 PG) (2,1) band, the O2 atmospheric (0,1) and (1,2) bands, and the N I 8680- and 8629-A multiplets. Photoelectron impact models adequately described the measured 1 PG profile but significantly underestimated the N I multiplet emission rates. It is suggested that the primary source of the multiplets is photodissociation of N2. The contribution of this process was estimated from a model based on the shape of the N I 1200-A lines photoexcitation cross section. If the proposed excitation mechanism is correct, peak cross-section values for the 8680- and 8629-A multiplets would have to be 7.2 ± 5.2 × 10−20 and 5.7 ± 3.2 × 10−20 cm2, respectively.