Scott A. Budzien

Tomographic studies of aeronomic phenomena using radio and UV techniques

Tomographic characterization of ionospheric and thermospheric structures using integrated line-of-sight measurements provides a unifying paradigm for the investigation of various aeronomic phenomena. In radio tomography, measurements of the total electron content (TEC) obtained using a chain of ground receivers and a transit satellite are inverted to reconstruct a two-dimensional electron density pro;le. Similarly, prominent optically thin UV emissions, such as 911 and 1356 = A produced by radiative recombination of O + , provide the means to obtain F-region electron densities from space-based spectroscopic measurements. The existence of a number of UV sensors in orbit and in planning stage provide the means to carry out such tomographic remote sensing investigations on global scales. The inherent non-ideal acquisition geometry of such remote sensing observations, however, results in limited-angle tomographic inverse problems that are both ill-posed and ill-conditioned. Furthermore, the intrinsic presence of noise, especially in the case of UV measurements, imposes challenges on conventional reconstruction methods. To overcome these limitations, we approach the solution of these inverse problems from a regularization standpoint. In particular, we apply regularization by incorporating appropriate edge-preserving regularizing functionals that enforce piecewise smoothness of the solution. This paper describes these techniques, investigates associated inversion issues, and demonstrates their applicability through a case study. c � 2002 Published by Elsevier Science Ltd.

The Remote Atmospheric and Ionospheric Detection System experiment on the ISS: Mission Overview

The Remote Atmospheric and Ionospheric Detection System (RAIDS) is a suite of three photometers, three spectrometers, and two spectrographs which span the wavelength range 50-874 nm and remotely sense the thermosphere and ionosphere by scanning and imaging the limb. RAIDS was originally designed, built, delivered, and integrated onto a NOAA TIROS satellite in 1992. After a series of unfruitful flight opportunities, RAIDS is now certified for flight on the Kibo Japanese Experiment Module-Exposed Facility (JEM-EF) aboard the International Space Station (ISS) in September 2009. The RAIDS mission objectives have been refocused since its original flight opportunity to accommodate the lower ISS orbit and to account for recent scientific progress. RAIDS underwent a fast-paced hardware modification program to prepare for the ISS mission. The scientific objectives of the new RAIDS experiment are to study the temperature of the lower thermosphere (100-200 km), to measure composition and chemistry of the lower thermosphere and ionosphere, and to measure the initial source of OII 83.4 nm emission. RAIDS will provide valuable data useful for exploring tidal effects in the thermosphere and ionosphere system, validating dayside ionospheric remote sensing methods, and studying local time variations in important chemical and thermal processes.

Update on the calibration and performance of the special sensor ultraviolet limb imagers (SSULI)

The Naval Research Laboratory has built give Special Sensor Ultraviolet Limb Imagers (SSULIs) for the Defense Meteorological Satellite Program. These sensors are designed to measure vertical intensity profiles of the Earths airglow in the extreme and far ultraviolet (800 to 1700 angstroms). The data from these sensors will be used to infer altitude profiles of ion, electron and neutral density. The first SSULI is scheduled to launch in 2000. An identical copy of the SSULI sensor called LORAAS was launched aboard the ARGOS spacecraft on February 23, 1999. Data from LORAAS will be used to verify the performance of the SSULI sensors, ground analysis software and validate the UV remote sensing technique. Together with the LORAAS instrument the SSULI program will collect data on the composition of the upper atmosphere for a complete solar cycle.

The tiny ionospheric photometer instrument design and operation

The Tiny Ionospheric Photometer (TIP) instrument is a small, space-based, photometer that observes the ionosphere of the earth at 135.6 nanometers. The TIP instrument will primarily observe the airglow emission of the nighttime ionosphere caused by the radiative recombination of atomic oxygen. In addition, the TIP instrument will observe the auroral region boundaries from the emission caused by electron impact excitation. Six TIP instruments will be launched and flown simultaneously as each one is a payload carried aboard the Republic of China Satellite (ROCSAT-3) spacecraft as part of the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) program a constellation built and operated by the country of Taiwan. Observations will be made from three orbital planes spaced 60 degrees apart each containing two TIP instruments. The instruments will be able to provide global coverage as well as system and data redundancy in their intended orbital configuration. Raw data from the TIP instruments will be used for the characterization of ionospheric electron density gradients to improve ionospheric modeling. Data from the TIP instruments can also be combined with the data from the other two payloads on board the spacecraft that are a radio beacon and a GPS occultation experiment to result in enhanced ionospheric measurements. The TIP instrument design had to solve several design challenges in order to achieve its intended science and mission requirements. In addition, the design had to address the operational constraints imposed by the spacecraft and the cost constraints of multiple units.

Ionospheric Spectroscopy and Atmospheric Chemistry (ISAAC) experiment on the Advanced Research and Global Observation Satellite (ARGOS): quick look results

The Ionospheric Spectroscopy And Atmospheric Chemistry Experiment is a high resolution mid-ultraviolet Ebert-Fastie spectrograph that is flying on the USAF Advanced Research and Global Observing Satellite (ARGOS, launched 23 February 1999). The instrument is designed to spectrally resolve the rotational structure of the nitric oxide bands, which will be used to infer the temperature in the lower thermosphere (90 - 200 km altitude range). The instrument is operated as a limb imager with a limb scan occurring every 100 seconds throughout the expected three year mission life. The ARGOS is in a sun-synchronous, near-polar orbit at 833 km altitude with an ascending node crossing time of 2:30 PM. We will present an overview of the instrument and discuss its calibration and in-flight performance.

Far ultraviolet equatorial aurora during geomagnetic storms as observed by the Low‐Resolution Airglow and Aurora Spectrograph

We report the detection of storm time enhancements in the low-latitude far ultraviolet airglow as observed by the Low-Resolution Airglow and Aurora Spectrograph on the Advanced Research and Global Observation Satellite. The enhancements are present in several of the dayside and nightside emission lines, including the prominent 1304- and 1356-A lines of atomic oxygen as well as the N2 Lyman-Birge-Hopfield bands near 1465 and 1495 A. Time histories of the average low-latitude intensities of all emissions show a correlation with geomagnetic activity, as measured by the Dst index. Comparisons between the prestorm and storm time latitude profiles indicate that the emission increases are confined to magnetic latitudes < 20°. We have used the ratio of 1356 A/1495 A as a measure of O/N2 composition changes at these low latitudes. Although this ratio shows composition changes during the storm, no change in the ratio is observed during the peak in the emission. On the basis of the emission morphology, we conclude that these emission enhancements are most likely the result of energetic neutral atoms, which are created in the ring current and collisionally excite ambient atomic oxygen and molecular nitrogen in the low-altitude, low-latitude ionosphere and thermosphere.

High-resolution Ionospheric and Thermospheric Spectrograph (HITS) on the Advanced Research and Global Observing Satellite (ARGOS): quick look results

The High-resolution Ionospheric and Thermospheric Spectrograph (HITS) is a very high resolution (> 0.5 angstroms resolution over the 500 - 1500 angstroms passband) Rowland circle spectrograph that is currently flying on the USAF Advanced Research and Global Observing Satellite (ARGOS, launched 23 February 1999). The ARGOS is in a sun- synchronous, near-polar orbit at 833 km altitude with an ascending node crossing time of 2:30 PM. The instrument is designed to spectrally resolve the 834 angstroms triplet to demonstrate a new technique for remotely sensing the electron density in the F-region ionosphere. In addition, the HITS can spectrally resolve the rotational structure of the N2 Lyman-Birge-Hopfield bands, which can be used to infer the thermospheric temperature. The HITS can resolve the radiative recombination continuum produced by recombining O+ ions and electrons, which can be used to infer the electron temperature. The HITS will also produce a high spectral resolution array of the 500 - 1000 angstroms passband to produce a more accurate identification of some of the previously unresolved features of the dayglow spectrum. The instrument operates as a limb imager with a limb scan occurring every 100 seconds throughout the expected three year mission life. Its field-of-view is 0.06 degree(s) X 4.6 degree(s), which corresponds to 3 km (altitude) X 230 km (along the horizon) at the limb. The instruments field-of-regard is 17 degree(s) X 4.6 degree(s), which covers the 100 - 750 km altitude range. We will present an overview of the instrument and discuss its calibration and in-flight performance.

On-orbit characterization and performance of the HIRAAS instruments aboard ARGOS: LORAAS sensor performance

The Advanced Research and Global Observation Satellite (ARGOS) has been operating since February 1999 and includes three spectrographs comprising the High Resolution Airglow and Auroral Spectroscopy (HIRAAS) experiment. The HIRAAS instruments remotely sense the Earths mid-, far- and extreme-ultraviolet airglow to study the density, composition, and temperature of the thermosphere and ionosphere. The Low Resolution Airglow and Aurora Spectrograph (LORAAS) is a limb scanner covering the 80-170 passband nm with 1.8 nm spectral resolution. Repeated serendipitous observations of hot O- and B-type stars have been used to improve the aspect solution, characterize the instrument field-of-view, and monitor relative sensitivity degradation of the instrument during the mission. We present the methodology of performance characterization and report the observed performance degradation of the LORAAS wedge-and-strip microchannel plate detector. The methods and results herein can be utilized directly in on-orbit characterization of the SSULI operational sensors to fly aboard the DMSP Block 5D3 satellites.

Using the unconventional stellar aspect (USA) experiment on ARGOS to determine atmospheric parameters by x-ray occultation

The Unconventional Stellar Aspect (USA) experiment is a multi-purpose experiment built around an X-ray sensor viewing celestial sources. The objectives include both basic research in X-ray astronomy and exploration of applied uses of X-ray sensors in space. The applied uses depend in large part upon exploiting understanding of celestial X-ray point sources. The experiment was launched on February 23, 1999 from Vandenberg AFB, CA aboard the Advanced Research and Global Observation Satellite (ARGOS). USA operated from April 1999 to November 2000. It consists of two proportional counters mounted in a two-axis gimbal for offset pointing from the nadir-pointed ARGOS. We present an overview of the experiment and then describe how it is used to provide a new atmospheric diagnostic that takes the form of redundant sets of atmospheric column density determinations. The data analyzed are energy-resolved photon extinction curves of X-ray celestial sources occulted by the Earths atmosphere. As each X-ray source is occulted by the mesosphere and lower thermosphere (80-160 km), the density profile is derived from the extinction curve and temperature is derived from the scale height; limited composition information may be derived from the energy- dependence of extinction. These data are compared to standard atmospheric models. This research is the first to study the neutral atmosphere using X-ray source occultations, and complements UV airglow remote sensing techniques used aboard ARGOS that are insensitive to nighttime neutral density.

Characterization of sensitivity degradation seen from the UV to NIR by RAIDS on the International Space Station

This paper presents an analysis of the sensitivity changes experienced by three of the eight sensors that comprise the Remote Atmospheric and Ionospheric Detection System (RAIDS) after more than a year operating on board the International Space Station (ISS). These sensors are the Extreme Ultraviolet Spectrograph (EUVS) that covers 550-1100 Å, the Middle Ultraviolet (MUV) spectrometer that covers 1900-3100Å, and the Near Infrared Spectrometer (NIRS) that covers 7220-8740 Å. The scientific goal for RAIDS is comprehensive remote sensing of the temperature, composition, and structure of the lower thermosphere and ionosphere from 85-200 km. RAIDS was installed on the ISS Japanese Expansion Module External Facility (JEM-EF) in September of 2009. After initial checkout the sensors began routine operations that are only interrupted for sensor safety by occasional ISS maneuvers as well as a few days per month when the orbit imparts a risk from exposure to the Sun. This history of measurements has been used to evaluate the rate of degradation of the RAIDS sensors exposed to an environment with significant sources of particulate and molecular contamination. The RAIDS EUVS, including both contamination and detector gain sag, has shown an overall signal loss rate of 0.2% per day since the start of the mission, with an upper boundary of 0.13% per day attributed solely to contamination effects. This upper boundary is driven by uncertainty in the change in the emission field due to changing solar conditions, and there is strong evidence that the true loss due to contamination is significantly smaller. The MUV and NIRS have shown stability to within 1% over the first year of operations.