R. L. Bishop

A statistical study of midlatitude spread F at Wallops Island, Virginia

[1] An ionosonde study using data from Wallops Island, Virginia (37.95°N, 284.53°E, 67.5° dip angle), over a full solar cycle from 1996 to 2006 has been conducted. A pattern recognition algorithm is used to analyze these ionograms in order to determine the statistics of midlatitude spread F. An ionogram displays spread F both horizontally and vertically, which are defined as range and frequency spread F, respectively. Range and frequency spreading can occur either simultaneously or separately. Seasonal and solar cycle variations have been studied using the data set; both are significant and are somewhat different for range and frequency spread F. Correlations of spread F duration with F 10.7, Kp, and AE are investigated. The results provide insights into causative sources for both types of midlatitude spread F.

Radiometer Calibration Using Colocated GPS Radio Occultation Measurements

We present a new high-fidelity method of calibrating a cross-track scanning microwave radiometer using Global Positioning System (GPS) radio occultation (GPSRO) measurements. The radiometer and GPSRO receiver periodically observe the same volume of atmosphere near the Earths limb, and these overlapping measurements are used to calibrate the radiometer. Performance analyses show that absolute calibration accuracy better than 0.25 K is achievable for temperature sounding channels in the 50-60-GHz band for a total-power radiometer using a weakly coupled noise diode for frequent calibration and proximal GPSRO measurements for infrequent (approximately daily) calibration. The method requires GPSRO penetration depth only down to the stratosphere, thus permitting the use of a relatively small GPS antenna. Furthermore, only coarse spacecraft angular knowledge (approximately one degree rms) is required for the technique, as more precise angular knowledge can be retrieved directly from the combined radiometer and GPSRO data, assuming that the radiometer angular sampling is uniform. These features make the technique particularly well suited for implementation on a low-cost CubeSat hosting both radiometer and GPSRO receiver systems on the same spacecraft. We describe a validation platform for this calibration method, the Microwave Radiometer Technology Acceleration (MiRaTA) CubeSat, currently in development for the National Aeronautics and Space Administration (NASA) Earth Science Technology Office. MiRaTA will fly a multiband radiometer and the Compact TEC/Atmosphere GPS Sensor in 2015.

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.

The Remote Atmospheric and Ionospheric Detection System on the ISS: sensor performance and space weather applications from the visible to the near infrared

The RAIDS experiment is a suite of eight instruments to be flown aboard the Japanese Experiment Module-Exposed Facility on the International Space Station (ISS) in late 2009. Originally designed, built, and integrated onto the NOAA TIROS-J satellite in 1993, the original RAIDS hardware and the mission objectives have been modified for this ISS flight opportunity. In this paper we describe the four near infrared instruments on the RAIDS experiment covering the wavelength range of 630 - 870 nm. Over the past two years these instruments have undergone modification, refurbishment, and testing in preparation for flight. We present updated sensor characteristics relevant to this new ISS mission and discuss performance stability in light of the long instrument storage period. The four instruments, operating in a limb scanning geometry, will be used to observe the spectral radiance of atomic and molecular emission from the Earths upper atmospheric airglow. The passbands of the photometers are centered on the atomic lines OI(777.4), OI[630.0], and the 0-0 band of O2 Atmospheric band at 765 nm. The spectrometer scans from 725 to 870 nm. These observations will be used in conjunction with the other RAIDS instruments to investigate the properties of the lower thermosphere and to improve understanding of the connections of the region to the space environment, solar energy flux and the lower atmosphere. These studies are fundamentally important to the understanding the effects of the atmosphere and ionosphere on space systems and their operation in areas such as satellite drag, communications and navigation.

GEOScan: A global, real-time geoscience facility

GEOScan is a proposed space-based facility of globally networked instruments that will provide revolutionary, massively dense global geosciences observations. Major scientific research projects are typically conducted using two approaches: community facilities, and investigator lead focused missions. While science from space is almost exclusively conducted within the mission model, GEOScan is a new concept designed as a constellation facility from space utilizing a suite of space-based sensors that optimizes the scientific value across the greatest number of scientific disciplines in the earth and geosciences, while constraining cost and accommodation related parameters. Our grassroots design processes target questions that have not, and will not be answered until simultaneous global measurements are made. The relatively small size, mass, and power of the GEOScan instruments make them an ideal candidate for a hosted payload aboard a global constellation of communication satellites, such as the Iridium NEXTs 66-satellite constellation. This paper will focus on the design and planning components of this new type of heterogeneous, multi-node facility concept, such as: costing, design for manufacture, science synergy, and operations of this non-traditional mission concept. We will demonstrate that this mission design concept has distinct advantages over traditional monolithic satellite missions for a number of scientific measurement priorities and data products due to the constellation configuration, scaled manufacturing and facility model.

Propagation of CubeSats in LEO using NORAD Two Line Element Sets: Accuracy and Update Frequency

Information on the orbital characteristics of satellites and other earth-orbiting objects is made available to the public in the form of two-line element sets (TLEs), published by the North American Aerospace Defense Command (NORAD). TLEs are typically not used alone for applications that require reliable and accurate position determination because TLEs are not accompanied by any indicators of accuracy or consistency. In this paper, we analyze the characteristics of TLE updates for CubeSats in low-Earth orbit (LEO) with respect to both update frequency and accuracy. We use both catalogued TLE data from July 2011 to July 2012 alone in a Monte Carlo analysis as well as compare TLE-only propagation with “truth” on-orbit GPS data from The Aerospace Corporation’s recent satellite mission, the PicoSatellite Solar Cell Testbed 2 (PSSCT-2), which launched in 20 July 2011 and operated until 8 December 2011. In addition to calculating the error statistics between the PSSCT-2 GPS positions and TLE propagated positions using the unusually frequent TLE updates available over the 213.5 minute period of time that GPS data is available, we also calculate error statistics as a function of less frequent TLE updates as well as calculate error statistics using a Monte Carlo simulation for TLE updates. From the latter we find that a CubeSat-class mission operating in a low orbit (under 350 km) using TLE propagation may be able to resolve position determination errors to as low as: in-track with mean = 0.177 km and standard deviation = 0.619 km; cross-track with mean = 0.108 km and standard deviation 0.619 km; and radial with mean = -0.068 km and standard deviation = 0.274 km, for a total mean = 0.832 km and standard deviation = 0.444 km.

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.

Assessment of Radiometer Calibration With GPS Radio Occultation for the MiRaTA CubeSat Mission

The microwave radiometer technology acceleration (MiRaTA) is a 3U CubeSat mission sponsored by the NASA Earth Science Technology Office. The science payload on MiRaTA consists of a triband microwave radiometer and global positioning system (GPS) radio occultation (GPSRO) sensor. The microwave radiometer takes measurements of all-weather temperature (V-band, 50-57 GHz), water vapor (G-band, 175-191 GHz), and cloud ice (G-band, 205 GHz) to provide observations used to improve weather forecasting. The Aerospace Corporations GPSRO experiment, called the compact total electron content and atmospheric GPS sensor (CTAGS), measures profiles of temperature and pressure in the upper troposphere/lower stratosphere (~20 km) and electron density in the ionosphere (over 100 km). The MiRaTA mission will validate new technologies in both passive microwave radiometry and GPSRO: 1) new ultracompact and low-power technology for multichannel and multiband passive microwave radiometers, 2) the application of a commercial off-the-shelf GPS receiver and custom patch antenna array technology to obtain neutral atmospheric GPSRO retrieval from a nanosatellite, and 3) a new approach to space-borne microwave radiometer calibration using adjacent GPSRO measurements. In this paper, we focus on objective 3, developing operational models to meet a mission goal of 100 concurrent radiometer and GPSRO measurements, and estimating the temperature measurement precision for the CTAGS instrument based on thermal noise Based on an analysis of thermal noise of the CTAGS instrument, the expected temperature retrieval precision is between 0.17 and 1.4 K, which supports the improvement of radiometric calibration to 0.25 K.

Observations of the migrating semidiurnal and quaddiurnal tides from the RAIDS/NIRS instrument

In this paper we analyze temperature data from the Near-Infrared Spectrometer (NIRS) instrument on Remote Atmospheric and Ionospheric Detection System experiment on the International Space Station and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on the Thermosphere Ionosphere Mesosphere Energetics Dynamics satellite during June and July 2010 to investigate structures of the migrating semidiurnal (12 h) and quaddiurnal (6 h) tides in the upper mesosphere and lower thermosphere. Temperature measurements from the NIRS and SABER instruments allow us to examine the tides from the stratosphere to the lower thermosphere. We find that the amplitude of the migrating 6 h tide grows from ~5 K near 100 km altitude to ~30 K near 130 km. The amplitudes of the tide at altitudes accessible by NIRS are much larger than those previously reported at lower altitudes from the Aura Microwave Limb Sounder and the SABER instruments. The amplitude of the 12 h tide in the NIRS data shows two peaks in the lower thermosphere (between 95 and 130 km) with a maximum around 60 K occurring in the winter hemisphere near 20° latitude and a second maximum around 40 K occurring in the summer hemisphere near 30° latitude. The structure of the migrating terdiurnal (8 h) tide is also investigated in the NIRS data and shows increasing amplitude with altitude over a broad range of latitudes, roughly between 50°N and 30°S. Altitudinal variations seen in the 6, 8, and 12 h tides suggest an evolving mix of various Hough modes.

Development of the Microwave Radiometer Technology Acceleration (MiRaTA) CubeSat for all-weather atmospheric sounding

The Microwave Radiometer Technology Acceleration (MiRaTA) is a 3U CubeSat mission sponsored by the NASA Earth Science Technology Office (ESTO). The science payload on MiRaTA consists of a tri-band microwave radiometer and GPS radio occultation (GPSRO) experiment. The microwave radiometer takes measurements of all-weather temperature (V-band, 52-58 GHz), water vapor (G-band, 175-191 GHz), and cloud ice (G-band, 207 GHz) to provide key observations used to improve weather forecasting. The GPSRO experiment, called the Compact TEC (Total Electron Content) and Atmospheric GPS Sensor (CTAGS) measures profiles of temperature and pressure in the upper neutral atmosphere and electron density in the ionosphere. The MiRaTA mission will validate new technologies in both passive microwave radiometry and GPS radio occultation: (1) new ultra-compact and low-power technology for multi-channel and multi-band passive microwave radiometers, (2) new GPS receiver and patch antenna array technology for both neutral atmosphere and ionospheric GPS radio occultation retrieval on a nanosatellite, and (3) a new approach to spaceborne microwave radiometer calibration using adjacent GPSRO measurements.