MIRO (Microwave Instrument for the Rosetta Orbiter) is a lightweight, uncooled, dual-frequency heterodyne radiometer. The MIRO encountered asteroid Steins in 2008, and during the flyby, MIRO used the Asteroid Mode to measure the emission spectrum of Steins. The Asteroid Mode is one of the seven modes of the MIRO operation, and is designed to increase the length of time that a spectral line is in the MIRO pass-band during a flyby of an object. This software is used to calibrate the continuum measurement of Steins’ emission power during the asteroid flyby.
The MIRO raw measurement data need to be calibrated in order to obtain physically meaningful data. This software calibrates the MIRO raw measurements in digital units to the brightness temperature in Kelvin. The software uses two calibration sequences that are included in the Asteroid Mode. One sequence is at the beginning of the mode, and the other at the end. The first six frames contain the measurement of a cold calibration target, while the last six frames measure a warm calibration target. The targets have known temperatures and are used to provide reference power and gain, which can be used to convert MIRO measurements into brightness temperature.
The software was developed to calibrate MIRO continuum measurements from Asteroid Mode. The software determines the relationship between the raw digital unit measured by MIRO and the equivalent brightness temperature by analyzing data from calibration frames. The found relationship is applied to non-calibration frames, which are the measurements of an object of interest such as asteroids and other planetary objects that MIRO encounters during its operation.
This software characterizes the gain fluctuations statistically and determines which method to estimate gain between calibration frames. For example, if the fluctuation is lower than a statistically significant level, the averaging method is used to estimate the gain between the calibration frames. If the fluctuation is found to be statistically significant, a linear interpolation of gain and reference power is used to estimate the gain between the calibration frames.
This work was done by Seungwon Lee of Caltech for NASA’s Jet Propulsion Laboratory.
The software used in this innovation is available for commercial licensing. Please contact Daniel Broderick of the California Institute of Technology at
This Brief includes a Technical Support Package (TSP).
MIRO Continuum Calibration for Asteroid Mode
(reference NPO-47075) is currently available for download from the TSP library.
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Overview
The document is a Technical Support Package from NASA's Jet Propulsion Laboratory (JPL) detailing the MIRO (Microwave Instrument for Rosetta Orbiter) Continuum Calibration for Asteroid Mode. It is part of the NASA Tech Briefs and is intended to disseminate results from aerospace-related developments with broader technological, scientific, or commercial applications.
The primary focus of the document is on the calibration of continuum measurements during asteroid flybys. The MIRO instrument is designed to measure the thermal emissions from celestial bodies, and the calibration process is crucial for ensuring accurate data collection. The document outlines the methodology used to assess the gains from two calibration sequences, specifically for millimeter and sub-millimeter wavelengths.
A hypothesis test was conducted to determine if the gains from the two calibration sequences (denoted as g1 and g2) come from the same distribution. The null hypothesis posited that the gains are from the same distribution. The t-statistic was calculated for the millimeter gains, resulting in a value of -6.6116, with a T-probability of 0.1191%. This low probability allowed for the rejection of the null hypothesis at a confidence level of 99.88%. Similar tests were performed for sub-millimeter LO-0 and LO-1 gains, leading to the conclusion that the null hypothesis could also be rejected for these sequences, indicating significant differences in the gains.
The document includes figures illustrating the actual gains calculated from the average temperature and power of measurements, highlighting the statistical noise present in the data. Linear interpolation was employed to estimate gains during observations, providing a smoother representation of the data.
Overall, the document emphasizes the importance of rigorous statistical analysis in the calibration process, ensuring that the MIRO instrument can provide reliable measurements during asteroid observations. It serves as a resource for researchers and engineers involved in similar calibration efforts and contributes to the broader understanding of thermal emissions from celestial bodies. The research was conducted under a contract with NASA, and the document is subject to export control regulations, reflecting its proprietary nature.
