----- Attempting Submission 1 (Tue May 08 01:16:14 GMT 2007) -----
This should be a duplicate (backup) of the immediately previous successful submission but
this submission initally failed. I logged out of and back into APT and attempting
this submission again now. Assigned ID: 675
----- Attempting Submission 2 (Sat Jan 27 00:43:13 GMT 2007) -----
Phase I Proposal 675 (phase16-GO) successfully submitted.
----- Attempting Submission 3 (Fri Feb 09 23:02:41 GMT 2007) -----
Phase I Proposal 675 (phase16-GO) successfully submitted.
Probing Uranus' Vertical Aerosol Structure at EquinoxAfter a decade of quiescence following the Voyager flybys, Uranus' atmosphere has been exhibiting increasing activity approaching equinox that suggests a short timescale, dynamical, response in addition to a long timescale, radiative, response to the seasonal change of hemispheric heating. We propose to investigate this dichotomy by measuring Uranus' vertical aerosol structure over the entire surface, including both poles, at equinox when the forcing insolation is hemispherically symmetric, requiring that the sub-Earth latitude be less than a degree. Only at equinox (every 42 years) can the entire surface of the planet be viewed (over a full rotation) and mapped with the same viewing geometry. We will probe the morphology of the vertical haze structure using NICMOS narrow band filters beyond 1 micron to isolate different altitude regimes between the stratosphere and cloud deck and investigate its change since Cycle 7. We will use two complementary approaches: First, imaging will be done using medium- and narrow-band filters first to locate the dynamically-produced discrete cloud features, then to probe their vertical structure and morphology. The methane absorption bands are stronger in the proposed near-IR (1 to 2.5 microns) than at shorter wavelengths, and the strong H2 pressure-induced absorption from 2.1-2.4 microns contributes to the peak opacity. This enhances the visibility of transient, spatially isolated features and allows their structure to be probed to higher altitudes; namely, to the upper troposphere where they would be evidence of convective overshoot, a dynamical manifestation that would support strong seasonally-induced static instability. In addition to probing the structure with filter photometry, we will measure longitudinal limb profiles to probe the vertical background haze distribution vs latitude. HST/NICMOS is required because it avoids telluric water absorption and OH+O2 emission, and has a stable, well-characterized PSF, essential for limb studies and extracting the vertical structure of fine features crossing the disk. The proposed observations would complement the ground-based Uranus equinox campaign.Our observations are driven by our objective to probe morphologically Uranus' vertical haze distribution. They rely on two standard approaches; namely, filter photometry at various wavelengths over which the atmospheric absorption coefficient varies widely, and on conventional center-to-limb (CTL) measurements, along lines of constant latitude (assumed longitudinally homogeneous), which probe vertical optical depths roughly equal to "mu", the direction cosine of the observer relative to the normal.
Longitudinal CTL measurements in conjunction with filter photometry will be used primarily to determine the background vertical haze structure vs latitude. However, the CTL measurements should also help to constrain the filter photometry of those discrete features that appear in overlapping images from more than one orbit that have, respectively, different secants relative to the observer. Probing Uranus' atmospheric haze depths requires observations in different narrow-band filters that sample different amounts of methane+H2 absorption. The filters have been chosen with these criteria in mind. The wide filters have been selected to search sensitively for the discrete dynamical features and to characterize their horizontal extent.
Filters and Exposure Times: The Phase 2 exposure times and overheads herein are close to those listed in the Phase 1 Table. Our filter choices and exposure times were dictated by lessons learned from earlier NICMOS observations (Cycle 7 GO 7429). These revealed the complexity of Uranus in the near IR: the images varied significantly from filter to filter (Karkoschka 1998, 2001). We select filters to systematically probe the vertical aerosol distribution that creates the observed diversity. Seven filters will be used in all four orbits. These filters provide high signal in short exposure times and are expected to show the best contrast. The feature drift from the planet's rotation is only about 1 pixel for these exposures, yielding a good PSF. Most of the other five filters require longer exposure times, thus they are only observed in one orbit each, using NIC2. Altogether, these filters constrain the albedo and CTL profiles at various absorption-strength methane and hydrogen wavelengths. The exposure times have been revised upwards for the longer-wavelength filters compared to Cycle 7 in order to obtain sufficient S/N to interpret discrete the features and the CTL profiles.
Exposure Pattern and Sequence: We will apply an extension of a technique to that used successfully in earlier NICMOS imaging (GO 7429). Total exposure times in each filter are split in half to record Uranus on two different parts of the chip. Each of these will be drizzled between two sub-positions (this number is limited by the overhead and needed S/N). These actions will allow us to fully recover data in all bad pixels and to subtract out the sky background, thermal emission, and dark current.
The exposure patterns are designed to minimize the overhead from telescope movements while providing for subtraction of sky and thermal array background and a recourse for removing bad pixel effects. At each pattern step, Uranus is being exposed somewhere within the aperture. The purpose of the primary pattern is background subtraction. It has two steps in X (instrument coordinates) separated by more than Uranus' 3."8 diameter to allow the subtraction. It is centered in the aperture. The sub-pattern is a 2-position dither in Y centered on the primary pattern position similarly offset in Y to avoid detector quad boundaries and to allow the removal of bad pixel and cosmic ray effects. In each orbit, we will take exposures of NIC1 filters first. To limit overhead, all filters for a given camera will be cycled before moving to the next pattern position. We will then switch to NIC2, run once through those filters at each primary and sub-pattern position to compete the orbit. For NIC1, the primary pattern avoids overlap of Uranus' image through use of a 5" nod centered on the 11" aperture so that these images can be subtracted to remove the sky and background. For NIC2, the primary pattern avoids overlap of Uranus' image through use of a 7" nod centered on the 19" aperture. The secondary pattern nods have similar amplitude but attempt to span an integral number of rows.
Each orbit is a separate visit. The four visits are grouped. The CML of the first visit is arbitrary. No orientation constraint is requested.We request that each of our four orbits to map Uranus' globe be separated by about 4.31 hours, corresponding to 90D of rotation of Uranus (The rotation period is 17.24+/-0.01 hrs) in order to obtain adequately uniform longitudinal sampling. Four approximately equally spaced orbits are requested, rather than three or two, in order to provide more overlapping longitudes that are observed at both high and low secants to help constrain the vertical haze distribution of the discrete features. This will also allow adequate sampling of the longitudinal dependence of the background vertical haze distribution by using the CTL variation along lines of constant latitude in order to test the longitudinal homogeneity of the haze vs latitude.
The timing of the first visit is broadly contrained to be that interval between Uranus Equinox (7 Dec) and the second ring plane crossing (16 Aug), which is near opposition (10 Sep), when both poles of Uranus are mostly visible from Earth while also both being mostly illuminated by the Sun, within a tolerance of 1.3 deg sub-Earth and subsolar latitude. Scheduling nearer to opposition within the schedulability window is desirable because it provides higher spatial resolution on Uranus' disk.
The remaining visits need not be sequential but they must occur within a couple of days of it, at quarter-revolution phases, to minimize relative longitudinal drift of clouds. This interval differs from the within 1 week request in Phase 1 and follows the recommendation of the TAC. If scheduling necessity dictates, one or more of the three follow-on phases may be postponed by a single Uranus rotation (period 17.24 hrs).
Cycle 16 is the ONLY year in which HST can get full pole-to-pole simultaneous imaging of the planet, to make a direct and unambiguous comparison of both poles.SOLAR SYSTEM12false0.0falsefalsefalsefalsefalsefalseSUPPORTEDSOLAR SYSTEMFirst target observed for this program. CML not constrained.
The disk-avg surface brightness varies from 0.70 to 0.00053 Jy per square arcsec
from F108N to F222M wavelengths; or (18 to 0.0033) E-14 erg/(cm2 s A)
per square arcsec.SURF(14000)=1.0 +/-0.5 E-14PLANETPLANET URANUSSTD=URANUSSOLAR SYSTEMCML about 90D greater than for URANUS-0SURF(14000)=1.0 +/-0.5 E-14PLANETPLANET URANUSSTD=URANUSSOLAR SYSTEMCML about 180D greater than for URANUS-0SURF(14000)=1.0 +/-0.5 E-14PLANETPLANET URANUSSTD=URANUSSOLAR SYSTEMCML about 270D greater than for URANUS-0SURF(14000)=1.0 +/-0.5 E-14PLANETPLANET URANUSSTD=URANUSNIC1ImagingNoNoF108NNIC1ImagingNoNoF110WNIC1ImagingNoNoF110MNIC1ImagingNoNoF113NNIC1ImagingNoNoF160WNIC1ImagingNoNoF165MNIC2ImagingNoNoF171MNIC2ImagingNoNoF187WNIC1ImagingNoNoF145MNIC1ImagingNoNoF108NNIC1ImagingNoNoF110WNIC1ImagingNoNoF110MNIC1ImagingNoNoF160WNIC1ImagingNoNoF165MNIC2ImagingNoNoF171MNIC2ImagingNoNoF187WNIC2ImagingNoNoF190NNIC1ImagingNoNoF108NNIC1ImagingNoNoF110WNIC1ImagingNoNoF110MNIC1ImagingNoNoF160WNIC1ImagingNoNoF165MNIC2ImagingNoNoF171MNIC2ImagingNoNoF187WNIC2ImagingNoNoF204MNIC1ImagingNoNoF108NNIC1ImagingNoNoF110WNIC1ImagingNoNoF110MNIC1ImagingNoNoF160WNIC1ImagingNoNoF165MNIC2ImagingNoNoF171MNIC2ImagingNoNoF187WNIC2ImagingNoNoF222MPOS-TARGBACKGROUNDDITHER25This NIC1 pattern is designed to minimize the overhead of telescope movements while providing recourse for bad pixels and subtracting sky and thermal array background. The main pattern avoids overlap of Uranus' 3."8 dia image while always collecting photons of the planet, through use of a 5" nod centered on the NIC1FIX aperture so that these images can be subtracted to remove the sky and background .
The sub-pattern is a 115-row 2-position dither to allow the removal of bad pixel and cosmic ray effects while avoiding quadrant bias offset effects. The filters for a given camera will be cycled before moving to the next position.NIC-YSTRIP-DITHtruetrue4.965120POS-TARGNIC-XSTRIP-DITH901truePOS-TARGBACKGROUNDDITHER27This NIC2 pattern is designed to minimize the overhead of telescope movements while providing recourse for bad pixels and subtracting sky and thermal array background. The main pattern avoids overlap of Uranus' 3."8 dia image while always collecting photons of the planet, through use of a 7" nod centered on the NIC2FIX aperture so that these images can be subtracted to remove the sky and background .
The sub-pattern is a 66-row 2-position dither to allow the removal of bad pixel and cosmic ray effects while avoiding quadrant bias offset effects. All filters for a given camera will be cycled before moving to the next pattern position.NIC-YSTRIP-DITHtruetrue4.973420POS-TARGNIC-XSTRIP-DITH902true/Users/lmt/Desktop/HSTCy16PhaseII/OP-cache/Cycle16Phase2-GO-v01.xmlThe timing of this visit is broadly contrained to be that interval between Uranus Equinox (7 Dec) and the second ring plane crossing (16 Aug), which is near opposition (10 Sep), when both poles of Uranus are mostly visible from Earth while also both being mostly illuminated by the Sun, within a tolerance of 1.3 deg sub-Earth and subsolar latitude. Near opposition provides the most spatial resolution.
The remaining visits will be tightly phased to this one, within a couple of days to minimize relative longitudinal drift of clouds, at quarter-rotation phases of Uranus. This differs from the within 1 week request in Phase 1 and follows the recommendation of the TAC. If scheduling necessity dictates, one or more of the three follow-on phases may be postponed by a single Uranus rotation (period 17.24 hrs).
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