The U.S. Naval Research Laboratory (NRL) has developed the Triple Tiny Ionospheric Photometer (Tri-TIP), an ultraviolet remote-sensing instrument based on the TIP. Tri-TIP measures emissions of atomic oxygen (Oi 135.6 nm) to determine plasma density in the nighttime ionosphere. The Tri-TIP design shrinks TIP to a 1U CubeSat form-factor and simplifies the mechanical design with a three-channel photometer system to isolate the target wavelength without a filter wheel. A heated strontium fluoride (SrF2) filter eliminates incoming light at wavelengths shorter than 135.6 nm. The filtered light is divided between two matched photometers by a beam splitter with a magnesium fluoride coating over aluminum (AlMgF2) deposited on 50% of the surface in a polka-dot pattern. The third photometer monitors dark count noise for later subtraction. One Tri-TIP configuration uses a beam splitter with a sapphire (Al2O3) substrate, which is opaque to wavelengths shorter than ∼140 nm, to later subtract contaminating emissions at wavelengths longer than 140 nm. A second Tri-TIP configuration uses a MgF2 substrate beam splitter to simultaneously measure Oi 135.6 nm from two adjacent fields-of-view. The performance of both beam splitters has been tested at NRL, and the results are presented.
The SSULI (Special Sensor Ultraviolet Limb Imager) is a limb-scanning far- and extreme-ultraviolet spectrometer flying on the Defense Meteorological Satellite Program (DMSP). The sensor sensitivity is tracked through the mission life by taking advantage of serendipitous stellar apparitions which, over the course of several days, track across the sensor’s field of view, allowing for not only the production of a sensitivity curve when compared against the known stellar spectra, but additionally pointing information and field-of-view information can be gleaned from comparing the star’s expected and observed positions. Most notably, because the star’s apparition traces across the field of view predictably in one axis, and randomly in another, multiple apparitions of these point sources can be used to map out the gain on the detector’s entire surface, revealing the existence and extent of localized gain sags. Additionally, multiple, routinized, and scheduled calibrations can be used to track sensor behavior through the mission life, including effects like a detector scrub, photocathode performance, and possible optics contamination. Results from the SSULI 002/DMSP F18 and SSULI 005/DMSP F19 stellar calibrations are presented.
The SSULI (Special Sensor Ultraviolet Limb Imager) is a low-resolution hyperspectral far and extreme ultraviolet limb-scanning
imager designed to monitor ionospheric and thermospheric airglow. SSULI has a spectral range from 80 to 170
nm, and a nominal resolution of 2.1 nm (at 147 nm). The instrument is scheduled to fly aboard all Defense
Meteorological Satellite Program (DMSP) Block 5D3 weather satellites. The first SSULI instrument was launched in
fall 2003, aboard the DMSP F16 flight, and has been collecting data since December 2003. The second SSULI flight
aboard DMSP F17 began in fall 2006. Early in the missions, both instruments began to observe intermittent but
significant periods of noise across the entire instrument passband, beyond the expected ion noise associated with sub-auroral
latitudes and the South Atlantic Anomaly. The morphology and intensity of the noise correlates strongly with
environmental conditions such as spacecraft potential. In order for the ground processing software to extract individual
emission features from the measured spectra, the data must be filtered for quality and the noise must be characterized on
short time scales and introduced as additional basis functions for use with the Multiple Linear Regression (MLR) feature
extraction algorithm. New algorithms, in the form of an Ion Noise Filter, have been developed for use with the MLR.
The techniques used in the Ion Noise Filter are discussed and examples of the successful extraction of spectra are
The SSULI (Special Sensor Ultraviolet Limb Imager) is a low-resolution hyperspectral far- and extreme-ultraviolet
limb-scanning imager designed to monitor ionospheric and thermospheric airglow. SSULI has a spectral range from 80
to 170 nm, and a nominal resolution of 2.1 nm (at 147 nm). The instrument is scheduled to fly aboard all DMSP Block
5D3 weather satellites. The first SSULI instrument was launched in fall 2003, aboard DMSP F16, and has been
collecting data since December 2003. The second SSULI flight aboard DMSP F17 began in fall 2006. On the ground,
the SSULI instruments are calibrated using a monochromator to isolate single emission features of interest produced by
a gas discharge lamp, whereas the flight spectra consists of numerous overlapping emissions. The determination of
individual emission feature contribution against the entire airglow spectrum is determined using the multiple linear
regression technique with basis functions defining each observable emission. The accuracy of the emission extraction
depends primarily on the ability to model the characteristics of the instrument line-shape, encompassing both optical
and electronic effects. In the course of developing the ground calibration algorithms, we are now able to produce line-shapes
much more faithful to the observed calibration features, as well as model instrument characteristics such as
scattered light and detector background components. This improved instrument characterization can then be passed to
the operational orbital emission extraction software to increase the fidelity of retrieved altitude profiles for observed
ultraviolet emissions. In addition, the techniques used with the ground calibration can monitor deviations in line-shape
and instrument sensitivity as a function of observed count rate, and these modified line-shapes can also be passed to the
ground analysis software. Validation of this method using SSULI 003 and 004 ground calibration data will be
The first of five Special Sensor Ultraviolet Limb Imager (SSULI) sensors was launched on the Defense Meteorological Satellite Program (DMSP) F16 spacecraft in October of 2003 into a sun-synchronous 830 km circular orbit at a local time of 0800-2000 UT. During initial sensor turn-on and evaluation, unusually high levels of background events were observed by the detector. The severity of this background is often sufficient to exceed the counting limit of the electronics as well as contribute to a rapid decrease in detector performance. In light of the SSULI performance degradation and concerns that the subsequent sensors may be affected in a similar manner, a "Tiger Team" investigation was launched to determine the source of the anomalous events. The conclusion from the investigation attributes the observed anomalous events to high levels of non-photon noise caused by ambient ions entering the instrument and striking the front microchannel plate. Additionally, the team made recommendations to mitigate the problem on future flights.