TWINS (Two Wide-angle Imaging Neutral-atom Spectrometers) is a Mission of Opportunity under NASA's Small Explorer (SMEX) program. TWINS-1 and TWINS-2 are the designations for NASA-sponsored instruments flying on unspecified non-NASA U.S. government spacecraft.

The TWINS-1 instrument high voltages were turned on in April 2007 and the TWINS-2 high voltages in May 2008; the exact launchdates are not available. The data (including both science data and spacecraft ephemeris/attitude information) from the two NASA-funded science instruments are publicly available to the scientific research community.  See http://twins.swri.edu/

TWINS is a stereo mission whose overall scientific objective is to establish the global connectivities and causal relationships between processes in different regions of the Earth.s magnetosphere. To meet this goal, TWINS-1 and TWINS-2 provide stereoscopic neutral atom imaging of the magnetosphere from two widely spaced, high-altitude, high-inclination spacecraft. TWINS instrumentation includes an energetic neutral atom (ENA) imager to capture charge-exchange-produced neutral atoms over a broad energy range (approximately 1-100 keV) and a Lyman-alpha detector to measure the density of the neutral hydrogen geocorona needed for extraction of magnetospheric ion fluxes from neutral atom data.

The TWINS-1 and TWINS-2 instruments are identical. Each spacecraft carrying TWINS instruments is in a Molniya orbit (63.4 deg, 7.2 Re apogee, 1000 km perigee; period 12 h), and is three-axis stabilized and approximately nadir-pointing. Each acquires image data with time resolution of 60 s. The time required to change actuator direction between scans (no data collection) was 25 seconds from June 2008 to July 2009, and 12 seconds at all other times.  This gives an effective cadence of 72 or 85 seconds.  The nominal design lifetime for each instrument is four years. TWINS operates  only during the apogee portion of each orbit, when the spacecraft is above the radiation belts.

More detailed information is available at the TWINS home page http://twins.swri.edu/

TWINS Spacecraft 1 - Neutral-atom Spectrometer Level-1 Magnetospheric Images and Image Movies at Full (9 Energy Steps and 15 minute) Resolution

Statistically smoothed TWINS image at 1 keV energy, in units of (cm^2 sr s eV)^-1. Images have been smoothed using a technique that provides approximately uniform statistics across the image.  Each image has 4x4 degree angular resolution and includes 15 minutes of data.

Statistically smoothed TWINS image at 4 keV energy, in the same format as the 1 keV smoothed image.

Statistically smoothed TWINS image at 8 keV energy, in the same format as the 1 keV smoothed image.

Statistically smoothed TWINS image at 12 keV energy, in the same format as the 1 keV smoothed image.

Statistically smoothed TWINS image at 16 keV energy, in the same format as the 1 keV smoothed image.

Statistically smoothed TWINS image at 20 keV energy, in the same format as the 1 keV smoothed image.

Statistically smoothed TWINS image at 25 keV energy, in the same format as the 1 keV smoothed image.

Statistically smoothed TWINS image at 30 keV energy, in the same format as the 1 keV smoothed image.

Statistically smoothed TWINS image at 50 keV energy, in the same format as the 1 keV smoothed image.

Statistically smoothed TWINS image movies at 1 keV energy, in units of (cm^2 sr s eV)^-1. Images have been smoothed using a technique that provides approximately uniform statistics across the image.  Each image has 4x4 degree angular resolution and includes 15 minutes of data.

Statistically smoothed TWINS image movie at 4 keV energy, in the same format as the 1 keV smoothed image.

Statistically smoothed TWINS image movie at 8 keV energy, in the same format as the 1 keV smoothed image.

Statistically smoothed TWINS image movie at 12 keV energy, in the same format as the 1 keV smoothed image.

Statistically smoothed TWINS image movie at 16 keV energy, in the same format as the 1 keV smoothed image.

Statistically smoothed TWINS image movie at 20 keV energy, in the same format as the 1 keV smoothed image.

Statistically smoothed TWINS image movie at 25 keV energy, in the same format as the 1 keV smoothed image.

Statistically smoothed TWINS image movie at 30 keV energy, in the same format as the 1 keV smoothed image.

Statistically smoothed TWINS image movie at 50 keV energy, in the same format as the 1 keV smoothed image.

The per-pixel sweep count is the  number of times a given pixel was  sampled by the instrument during thetime taken to make the image.  This value is only a function of   longitude (actuation angle), and so is the same for all latitude (imaged) pixels at a given scan (actuation) angle. The value is nominally the same for all pixels in an image, and is the same as the number of sweeps in the  image.  Differences from this value are due to errors in either actuator motion or transmission of data from agiven direction. 

Target value for the number of counts per pixel used in the smoothing algorithm. This value can vary by energy.

Array of energy values (in keV) for the smoothed images.  Nominally 1, 4, 8, 12, 16, 20, 25, 30, and 50 keV. 

[LIST ONLY] version of the smoothing algorithm used to create the TWINS_SMOOTH_IMAGE.

Longitude (deg) at the middle of the  first pixel.  For 4 deg pixel_size this is nominally -88 degrees.

Longitude (deg) at the middle of the  last pixel.  For 4 deg pixel_size this is nominally -92 degrees.

Latitude (deg) at the middle of the  first pixel.  For 4 deg pixel_size this is nominally 4 degrees.

Latitude (deg) at the middle of the  last pixel.  For 4 deg pixel_size this is nominally 88 degrees.

start time of the image and the stop time of the image in Modified Julian Date (MJD)

TWINS smoothed image error image at 1 keV energy.  The error in the flux for each pixel is given by sqrt(counts) / counts using the counts included in each pixel of the image. 

TWINS smoothed image error image at 4 keV energy, in the same format as the 1 keV smoothed image error image.

TWINS smoothed image error image at 8 keV energy, in the same format as the 1 keV smoothed image error image.

TWINS smoothed image error image at 12 keV energy, in the same format as the 1 keV smoothed image error image.

TWINS smoothed image error image at 16 keV energy, in the same format as the 1 keV smoothed image error image.

TWINS smoothed image error image at 20 keV energy, in the same format as the 1 keV smoothed image error image.

TWINS smoothed image error image at 25 keV energy, in the same format as the 1 keV smoothed image error image.

TWINS smoothed image error image at 30 keV energy, in the same format as the 1 keV smoothed image error image.

TWINS smoothed image error image at 50 keV energy, in the same format as the 1 keV smoothed image error image.

Statistically smoothed TWINS error image movie at 1 keV energy.  The error in the flux for each pixel is given by sqrt(counts) / counts using the counts included in each pixel of the image. 

Statistically smoothed TWINS error image movie at 4 keV energy, in the same format as the 1 keV smoothed error image.

Statistically smoothed TWINS error image movie at 8 keV energy, in the same format as the 1 keV smoothed error image.

Statistically smoothed TWINS error image movie at 12 keV energy, in the same format as the 1 keV smoothed error image.

Statistically smoothed TWINS error image movie at 16 keV energy, in the same format as the 1 keV smoothed error image.

Statistically smoothed TWINS error image movie at 20 keV energy, in the same format as the 1 keV smoothed error image.

Statistically smoothed TWINS error image movie at 25 keV energy, in the same format as the 1 keV smoothed error image.

Statistically smoothed TWINS error image movie at 30 keV energy, in the same format as the 1 keV smoothed error image.

Statistically smoothed TWINS error image movie at 50 keV energy, in the same format as the 1 keV smoothed error image.

Indication of the quality of the data based on three parameters. The quality flag is a 3 bit number. A value of 0 indicates good data.  A value of 1 indicates an attitude shift of more than 4 degrees during the sweep.  A value of 2 indicates that the Sun is within 20 degrees of the instrument...s FOV.  A value of 4 indicates a high level of background. A value of 7 would indicate that all three flags have been raised (indicating that caution should be used in interpreting this data).

A flag that identifies when attitude and ephemeris information are available. A value of 0 indicates data are available; a value of 1 indicates that either attitude or ephemeris information is not available for a given time interval.

Attitude Variation (degrees) during the time interval of each image. 

The change (in degrees) of the spacecraft attitude vector over the time required to make the given image.

Average spacecraft position vector in ECI coordinates (time series)

The average spacecraft location vector over the time interval of the image in ECI coordinates (cartesian XYZ components). 

The average polar pointing vector over the time interval of the image in ECI coordinates (Cartesian XYZ components). The polar attitude vector points to 90 degree instrument polar (imaged) angle.

The average azimuthal pointing vector over the time interval of the image in ECI coordinates (Cartesian XYZ components). The azimuthal pointing vector points to +90 degree instrument scan angle. 

The average location of the Sun over the time interval of the image in ECI coordinates (Cartesian XYZ components). 

The average geomagnetic dipole vector over the time interval of the image in ECI coordinates (Cartesian XYZ components). 

The average spacecraft location vector over the time interval of the image in SM coordinates (Cartesian XYZ components). 

The average polar pointing vector over the time interval of the image in SM coordinates (Cartesian XYZ components). The polar attitude vector points to 90 degree instrument polar (imaged) angle.

The average azimuthal pointing vector over the time interval of the image in SM coordinates (Cartesian XYZ components). The azimuthal pointing vector points to +90 degree instrument scan angle. 

The average location of the Sun over the time interval of the image in SM coordinates (Cartesian XYZ components). 

The average geomagnetic dipole vector over the time interval of the image in SM coordinates (Cartesian XYZ components). 

Spacecraft radial distance (in Earth radii)from the center of the Earth.

The McIlwain L-Shell at the spacecraft location assuming a dipole magnetic field model and using SM coordinates. 

Array of energy values (in keV) for the images.  Nominally 1, 4, 8, 12, 16, 20, 25, 30, and 50 keV. 

0 for a Differential Energy Flux image. 1 for an All Energies image

[LIST ONLY] Start and stop times of the image, along with the selected number of sweeps. 

TWINS raw image at 1 keV energy, in units of (cm^2 sr s eV)^-1.  These images are derived on the ground from direct events measurements of the time of flight and detection location on the anode for individual ENAs.  Each image has 4x4 degree angular resolution and includes 15 minutes of data. The first dimension of the image represents the scan angle in instrument coordinates.  In this system the azimuthal attitude vector points to +90 degree scan angle.  The second is the imaged angle, where 90 degrees is the central viewing angle of the instrument and the direction of the polar attitude vector.

TWINS raw image at 4 keV energy, in the same format as the 1 keV image.

TWINS raw image at 8 keV energy, in the same format as the 1 keV image.

TWINS raw image at 12 keV energy, in the same format as the 1 keV image.

TWINS raw image at 16 keV energy, in the same format as the 1 keV image.

TWINS raw image at 20 keV energy, in the same format as the 1 keV image.

TWINS raw image at 25 keV energy, in the same format as the 1 keV image.

TWINS raw image at 30 keV energy, in the same format as the 1 keV image.

TWINS raw image at 50 keV energy, in the same format as the 1 keV image.

A series of TWINS raw images at 1 keV energy. These are the same images as in the twins_image_e1 variable.

A series of TWINS raw images at 4 keV energy. These are the same images as in the twins_image_e2 variable.

A series of TWINS raw images at 8 keV energy. These are the same images as in the twins_image_e3 variable.

A series of TWINS raw images at 12 keV energy. These are the same images as in the twins_image_e4 variable.

A series of TWINS raw images at 16 keV energy. These are the same images as in the twins_image_e5 variable.

A series of TWINS raw images at 20 keV energy. These are the same images as in the twins_image_e6 variable.

A series of TWINS raw images at 25 keV energy. These are the same images as in the twins_image_e7 variable.

A series of TWINS raw images at 30 keV energy. These are the same images as in the twins_image_e8 variable.

A series of TWINS raw images at 50 keV energy. These are the same images as in the twins_image_e9 variable.

TWINS error image for raw image at 1 keV energy. The error in the flux for each pixel is based on the error in the fit of flux vs energy used to determine the flux value given in the primary image. 

TWINS raw error image at 4 keV energy, in the same format as the 1 keV error image.

TWINS raw error image at 8 keV energy, in the same format as the 1 keV error image.

TWINS raw error image at 12 keV energy, in the same format as the 1 keV error image.

TWINS raw error image at 16 keV energy, in the same format as the 1 keV error image.

TWINS raw error image at 20 keV energy, in the same format as the 1 keV error image.

TWINS raw error image at 25 keV energy, in the same format as the 1 keV error image.

TWINS raw error image at 30 keV energy, in the same format as the 1 keV error image.

TWINS raw error image at 50 keV energy, in the same format as the 1 keV error image.

A series of TWINS raw error images at 1 keV. These are the same images as in the error_image_e1 variable.

A series of TWINS error images at 4 keV. These are the same images as in the error_image_e2 variable.

A series of TWINS raw error images at 8 keV. These are the same images as in the error_image_e3 variable.

A series of TWINS raw error images at 12 keV. These are the same images as in the error_image_e4 variable.

A series of TWINS raw error images at 16 keV. These are the same images as in the error_image_e5 variable.

A series of TWINS raw error images at 20 keV. These are the same images as in the error_image_e6 variable.

A series of TWINS raw error images at 25 keV. These are the same images as in the error_image_e7 variable.

A series of TWINS raw error images at 30 keV. These are the same images as in the error_image_e8 variable.

A series of TWINS raw error images at 50 keV. These are the same images as in the error_image_e9 variable.


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