A collaboration between scientists and engineers at the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado at Boulder and Space Instruments (SI) has developed a six-channel, low-noise, highly stable electrometer ASIC. The ASIC is a mixed-signal (analog and digital), analog-to-digital converter on
a single chip. Designed specifically to interface with an array of photodiodes, the ASIC is ideal for use in low-light level
spectrometers or other applications where there are multiple low-level current sources.
Recognizing that the solar extreme ultraviolet (EUV) irradiance is an important driver of space weather, the National
Oceanic and Atmospheric Administration (NOAA) has added an Extreme Ultraviolet Sensor (EUVS) to its
Geostationary Operational Environmental Satellite (GOES) program, starting with the recently launched GOES-N, now
designated GOES-13. For the GOES-R series (slated for launch starting in 2015) , the EUVS measurement concept has
been redesigned. Instead of measuring broad bands spanning the EUV, the GOES-R EUVS will measure specific solar
emissions representative of coronal, transition region, and chromospheric variability. From these measurements, the
geo-effective EUV wavelength range from 5 to 127 nm can be reconstructed using models based on spectrally resolved
measurements gathered over the full range of solar variability. An overview of the GOES-R EUVS design is presented.
A description of the in-flight degradation tracking utilizing similar measurement and modeling techniques used to
generate the EUV irradiance is also provided.
The X-Ray Sensor (XRS) has been making observations of the solar soft X-ray irradiance for over thirty years onboard National Oceanic and Atmospheric Administration's (NOAA) Geostationary Operational Environmental Satellites (GOES). The XRS provides critical information about the solar activity for space weather operations, and the standard X-ray classification of the solar flares is based on its measurements. The GOES-R series of XRSs, with the first in the
series to launch in 2014, has a completely new instrument design. The XRS spectral bands remain the same as before by providing the solar X-ray irradiance in the 0.05-0.4 nm and 0.1-0.8 nm bands. The changes include using Si photodiodes instead of ionization cells to improve performance, using multiple channels to allow wider dynamic range, providing quadrant photodiodes for real-time flare location measurements, and providing accurate radiometric calibrations using
the National Institute of Standards and Technology (NIST) Synchrotron Ultraviolet Radiation Facility (SURF) in Gaithersburg, Maryland.
The first of the Geo-stationary Operational Environmental Satellites (GOES) -NO/P series, built
by Boeing Satellite Systems was launched on May 24, 2006. The spacecraft, now on-orbit and referred as
GOES-13, carries an Earth Imager, Sounder and a collection of space environment monitors (SEM)
including, for the first time, a solar Extreme Ultraviolet (EUV) telescope. The five-channel EUV telescope
measures the solar EUV energies in five wavelength bands from 5 nm to 135 nm.
We analyze the data from the five EUV channels, collected by the Post Launch Telemetry (PLT)
tests, and compare it to the predictions of precise optical models of the instrument, using two modeling
software- ZEMAXI and FREDII . From our models we detected a misalignment between the SXI and the
XRS/EUV bore-sights that were off by approximately 0.25 degree.
The reference solar irradiation between 1-140 nm in our model was acquired from the TIMED
data taken at the same time as the GOES data. When corrected by the appropriate calibration factors, all 5
channels agreed reasonably well with the TIMED data at zero degree angle of incidence. As expected, the
instruments' responses changed by more than 5% as a function of azimuth angles away from the Sun
center. These changes in irradiation values as a function of angle could be corrected to the values at normal
incidence using photometrical accurate optical models of the EUV instrument.
The Solar Dynamics Observatory (SDO) Extreme ultraviolet Spectro-Photometer (ESP), as a part of the Extreme
ultraviolet Variability Experiment (EVE) suite of instruments, was calibrated at the National Institute
of Standards and Technology (NIST) on the Synchrotron Ultraviolet Radiation Facility (SURF) Beam Line 2
in February 2007. Precise ESP alignment to the SURF beam was achieved through successive scans in X, Y,
Pitch and Yaw, using a comparison of the four channels of the ESP quad photodiode as a measure of alignment.
The observed alignment between the ESP and the other instruments in the EVE package was found to be in
very good agreement with that measured at the Laboratory for Atmospheric and Space Physics (LASP) at the
University of Colorado during ESP/EVE integration. The radiometric calibration of the ESP photometers in
the spectral range around 4.4 nm (central zeroth order), and the four first order channels centered at about
18.9, 25.4, 29.8, and 36.1 nm was performed with SURF synchrotron radiation. The co-alignment of the SURF
beam and the ESP optical axis for each energy and injected current was determined based on quad diode (QD)
photometer responses (photodiode count-rate data). This determined beam position was later used to obtain
exact energy-wavelength-flux profiles for each of the calibration energies and to calculate the quantum efficiency
of the ESP channels. The results of this calibration (quantum efficiencies) are compared to the previous ESP
NIST calibration results at SURF Beam Line 9 and to SOHO/SEM efficiencies.
Solar EUV irradiance plays a critical role in the variability of the upper atmosphere and ionosphere of Earth. Many
systems are impacted by these terrestrial changes including radio communication, GPS navigation, and satellite orbits.
Monitoring the solar EUV irradiance in the past has been left to research satellites and there have been long periods
where gaps in the observational record make it difficult to study and understand the long-term trends and impacts on
Earth. The National Oceanic and Atmospheric Administration (NOAA) has, for the first time, included an EUV Sensor
(EUVS) on the Geostationary Environmental Operational Satellite (GOES). This EUV Sensor (EUVS), launched in
May 2006, is design to provide the solar EUV irradiance information most critical to understanding and modeling
Earth's upper atmosphere. The EUVS has five broad EUV channels between 5 and 125 nm. It uses transmission
gratings and thin-film filters for wavelength discrimination and silicon diodes for detectors. The EUVS was extensively
calibrated at the Brookhaven National Labs Synchrotron Light Source with calibration standards traceable to NIST. It
samples the solar irradiance every ten seconds on a continuous basis from geosynchronous orbit. This paper will provide
an overview of the EUVS design, calibration, and performance results.
We report the design and laboratory testing of a prototype dual-grating filter-free extreme ultraviolet (EUV)
spectrometer that has potential as a highly stable instrument for measuring absolute solar irradiance in the X-ray through
far ultraviolet spectral range. The instrument is based on the same freestanding transmission gratings and silicon
photodiodes used on the successful Solar EUV Monitor (SEM) aboard SOHO and the EUV Spectrophotometer (ESP)
part of the EVE instrument suite to be flown on SDO. Its two gratings, placed in series, along with a simple baffle
structure provide excellent out of band "white" light rejection. Because the instrument does not use any thin film filters
or reflective optics it is not susceptible to the degradation and instability associated with such optical elements. We
present photometric efficiency data from laboratory tests with a Helium and Hydrogen discharge light source and
measurements of "white" light rejection taken using the Mt Wilson Observatory 60' solar telescope.
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