GLIMS Update: NPP satellite orbit

[kargel at hwr.arizona.edu]

Dear GLIMS colleagues,

A request for information has been issued by the Terra and NPP Project
scientists and the U.S. ASTER Science Team leader; these officials have passed
on the following message regarding a possible shift of the planned (luanch
2008)NPP satellite (orbit from a morning to afternoon orbit.  This may be an
issue for GLIMS, because the polar orbiting NPP will carry a MODIS-like
instrument (400 m spatial resolution, multiband across VIS, NIR, SWIR, and
TIR).  They have also requested information about the likely impacts on our
science.  My sense is that glacier observations would have gains and losses
from the possible orbit shift, but that the net would be a significant loss.
This is mainly due, in my consideration, to the typical increase in convective
cloudiness and the rise in temperature and moistuire content of the atmosphere
during the day; it is exhibited commonly as an increase through the day of cloud
cover, cloud optical depth, and cloud elevation in many alpine regions,
especially during the summer or during the other optimum imaging
seasons.  In some regions, the effects of daytime cloud buildup would render
glacier observations extremely difficult.  Of course, there are places and times
when morning clouds become thinner, fewer, or dissipate entirely during the day,
as I just had the pleasure to experience in the Wrangell Mountains 2 weeks ago.

There are other negative impacts, including loss of direct temporal (time of
day) comparability with MODIS observations timed with ASTER observations
(assuming ASTER and MODIS continue to function during the period
of NPP operations, which should begin in 2008; I note that ASTER is now slated
to continue operations through 2009 and may continue thereafter with any luck).
Maybe more profoundly, there is a strong chance of a cascading impact on
inter-instrument data comparability and the orbits of future environmental
missions; I anticipate that the desire to establish inter-instrument data
comparability (for data fusion) will tend to push future environmental
satellites, including any possible ASTER/Landsat follow-on, toward whatever
orbit NPP will have.  For future multi-decadal comparability with ASTER's and
Landsat 7's historic observations, a morning orbit for NPP would thus be
preferred, as it would tend to reinforce morning orbits for future observing
systems. Benefits from the planned orbit shift to afternoon would include
decreased afternoon snow cover as compared to morning snow (afternoon loss of
light night-time dustings of snow, for instance).  The tendency toward
disconnection of observations made in the morning and afternoon include changes
in temperature, changes in the
wetness of snow and its impact on multispectral classifiers, and changes in
illumination (contrast, shadows, potential for shape-from-shading,
directionality of illumination and hence directionality of observed
micro-features).  These illumination issues are not devastating for our
GLIMS work, but they are significant, especially if an afternoon orbit of NPP
propagated into an afternoon orbit of a Landsat or ASTER follow on.  The cloud
issues, however, would severely limit the applicability of NPP VIS/NIR/SWIR/TIR
data for our GLIMS work in many regions.

I seek your opinions, and if I have omitted some important reasons for
maintaining a morning orbit, or if I have come to the wrong conclusion, please
let me know.  If anybody may have a quantitative dataset or a powerful
empirical observation that may reinforce your perspective, please provide that
(or a link to it).

Sincerely,

Jeff Kargel


-----Original Message-----
From: Jon Ranson [mailto:kenneth.j.ranson at nasa.gov]
Sent: Thursday, August 11, 2005 5:05 AM
To: b.a.wielicki at larc.nasa.gov; djd at jord.jpl.nasa.gov;
vince.salomonson at gsfc.nasa.gov; jim at atmosp.physics.utoronto.ca;
mike at lithos.jpl.nasa.gov; gille at acd.ucar.edu; tsay at climate.gsfc.nasa.gov;
gwb at jord.jpl.nasa.gov; jon at taiga.gsfc.nasa.gov;
dherring at climate.gsfc.nasa.gov; edwards at ucar.edu; ziskin at ucar.edu;
jxiong at ltpmail.gsfc.nasa.gov
Subject: Fwd: Comments of moving NPP to an afternoon orbit


>Hello,

There is a move afoot to move the NPOES Preparatory Program (NPP) orbit to
the afternoon.  Jim Geason the NPP Project Scientist is seeking comments ont
he science implications of this change in the mission.  His message was sent
the the MODIS team, but I thought I would included the rest of the Terra
folks just in case.  Please send comments to Diane Wickland and Jim Gleason
with a CC to me.

Thanks,
Jon


>To:     NPP Science Team Members
>         MODIS Science Team Members
>         AIRS Science Team Members
>         AMSU/HSB Science Team Members
>         OMI  Science Team Members
>
>From:   Diane Wickland/ NPP Program Scientist
>         Jim Gleason/ NPP Project Scientist
>
>Subject: Quantifying the effect on the science data products from changing
the
>         NPP equator crossing time from 10:10am to 1:30pm
>
>
>As many of you have already heard the NPP launch date is slipping due
>to technical problems with some of the NPP instruments.  The current
>best estimate of the launch slip is 18 months with a new launch date
>of April 2008.  EOS Terra is currently beyond its engineering design
>lifetime, however the spacecraft and instruments are working well and
>the spacecraft has enough on-board consumables to last at least until
>2009.  Given the current slip, there is a reduced chance of significant
>data product overlap with the EOS Terra instruments and potentially
>greater data product overlap with the EOS Aqua and Aura instruments.
>
>The NPP Project Science leadership is considering the risks and
>benefits to the mission  science goals of moving NPP from a morning
>(10:30) crossing time to an early afternoon (1:30pm) crossing time.
>The NPP mission sciences goals can be summarized as, "Continue the
>scientific data record started  in the "EOS era."  Simply put, what are
>the scientific implications of considering NPP as a Aqua follow-on, not
>as a Terra follow-on?  What are the implications of a potential gap in
>the morning time series data stream?
>
>As members of the EOS and NPP science teams, you have been working with
>data from the EOS and Landsat spacecraft and hopefully are looking
>forward to continuing those observation using NPP and NPOESS data.
>What we would like to receive your assessment of the risks and benefits
>to answering your science questions if NPP is moved to an afternoon
>orbit?  We would like your input to be as quantitative as possible,
>hopefully illustrating your points with Terra, Aqua or Landsat data.
>Some example areas that we need to consider include;
>
>           temporal studies, using data from both morning and afternoon
> platforms,
>
>           coverage questions, What are the relative amounts of data
> lost due to systematic poor observing conditions in the morning or
> afternoon, i.e. data loss due to sun glint or persistent cloudiness,
>
>            cross platform calibration, data sets that require platform
> overlap with either Terra or Aqua,
>
>           evaluation of the effects on the morning time series (e.g.,
> of substituting afternoon MODIS data into the sequence to fill any
> gaps between Terra MODIS and the first morning NPOESS)
>
>           synergistic uses with other instruments on other platforms



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