Hyperspectral Images of Uranus

Hyperspectral Images of Uranus with STIS (Uranus-STIS)

Karkoschka & Tomasko (2009), Sromovsky et al. (2014), Sromovsky et al. (2018)

Fig. 11 from Sromovsky et al. (2018) showing composite images of the disk of Uranus for 2002 (A: left), 2012 (B: middle), and 2015 (C: right). The right half of each image is a color composite of fitted center-to-limb smoothed images, using the color assignments R=930 nm (methane), G=834.6 nm (methane + hydrogen), and B=826.8 nm (mostly hydrogen). The left half shows shows rotation-corrected H-band images from the NIRC-2 instrument on the Keck-II telescope.

Uranus-STIS is a collection of hyperspectral cubes of Uranus, constructed from HST/STIS observations which were obtained in 2002, 2012, and 2015. These data cover half the extent of Uranus with a spatial sampling of 0.0277 arcsec/pixel, and a spectral coverage from 300.4—1020.0 nm with a sampling of 0.4 nm/pixel. The published papers analyze the composition, dynamics and other physical properties of cloud bands on Uranus, using a combination of STIS spectra, HST imaging, and ground-based imaging and spectroscopy.

The data provided in this collection were obtained with the STIS 0.10" long-slit, which was aligned with the planet's polar axis and stepped across the disk at intervals of 0.152" from center to edge. This observing pattern was executed for both the G430L and G750L gratings. The data were pipeline processed, extracted, calibrated, and combined (see Sromovsky et al. 2018 and references therein), with the uniform spatial and spectral sampling noted above. Note that Uranus rotated more than 45° during the course of the observations, so any analysis of these data would have to presume a high degree of zonal symmetry.

Description of Data Products

Each of the three hyperspectral cubes are stored in multi-extension FITS files. Hyperspectral cubes have two spatial and one dispersion dimension. The spatial longitude and latitude dimensions are all 75×150 pixels, respectively; the spectral dimension (extensions 1 and 2) is 1800 pixels. The image extensions correspond to various quantities, all but the first of which contain coordinate information, as described in Table 1 below.

Table 1
Extension Name	Dimensions	Content
SCI	75×150×1800	Calibrated spectral radiance in dimensionless I/F
WAVELENGTH	1800	Spectral dispersion coordinate (nm)
LAT_CENTRIC	75×150	Planetocentric latitude (deg)
LAT_GRAPHIC	75×150	Planetographic latitude (deg)
REL_LON_EAST	75×150	Planet longitude relative to the central meridion (deg)
MU_OBS_COS	75×150	Cosine of the observer zenith angle
MUZ_SUN_COS	75×150	Cosine of the solar zenith angle
AZIMUTH	75×150	Angle between projections of the vectors from the sun to Uranus, and from Uranus to the observer, onto the tangent plane at the observed location on the planet (deg)

The spectral intensity I/F is the ratio, as a function of wavelength, of the observed radiance to that of a normally-illuminated Lambertian reflector at the same distance from the sun as the target.

The dispersion relation is defined by WCS keywords in the header of the SCI extension, but discrete values appear in the WAVELENGTH extension; they are equivalent at the center of each pixel, and both forms are included for convenience. An approximation to the planetographic coordinate system is represented in one of the FITS WCS systems, with the label "G". These coordinates are for convenience only: actual coordinates should be taken from the image extensions that contain the computed planet coordinates. See the README file for details.

An example IDL program, uranus-stis_read_example.pro, is provided to illustrate how to access the pixel data and coordinate information from the science files, to display an average of the image over a particular range of wavelengths, and to plot the spectrum over a range of planetographic coordinates.

The FITS primary headers include all the constituent STIS observation IDs that were combined to produce the merged spectrum, in keywords with names like ROOTNMnn.

Data Access

This HLSP collection is available via this DOI: dx.doi.org/10.17909/T9KQ4N. Alternatively, download the individual FITS files via links in Table 2 below.

Table 2
Epoch	HST Program	Description Paper	Sub-obs. latitude	File
2002-Aug.	GO–9035	Karkoschka & Tomasko (2009)	20.5° S	FITS file
2012-Sep.	GO–12894	Sromovsky et al. (2014)	19.5° N	FITS file
2015-Oct.	GO–14113	Sromovsky et al. (2018)	31.7° N	FITS file

Please remember to cite the appropriate paper(s) above and the DOI if you use these data in a published work.

Note: These HLSP data products are licensed for use under CC BY 4.0.