# Comments can be added freely as lines starting with '#'
# 'sigma.txt' is the replacement for 'weights.txt', and renders it
# obsolete. It is similar to 'weights.txt', but extends its capabilities.
# 'sigma.txt' allows you to set up rules describing the default
# uncertainties in position, time, and magnitude for astrometric data.
# The idea is that you can tell Find_Orb that all observations from a
# given observatory over a given time span and magnitude range have,
# by your estimate, specific uncertainties in those three quantities.
# The resulting uncertainties are simply default values, used when
# there's no other way to know the uncertainty. If you use the
# AstDyS/NEODyS .rwo format, the data have astrometric uncertainties
# given with each observation. And Find_Orb provides ways to specify
# uncertainties via special keywords within the observations. See
# for details.
# This is a revised version of what used to be 'weight.txt'. That
# file was quite similar, except that instead of storing uncertainties,
# weights were stored. These basically just boiled down to 1/sigma_posn,
# with sigma_posn expressed in arcseconds. Also, only sigmas for
# position could be defined; 'sigma.txt' adds sigmas for magnitude
# and time as well; and allows you to specify a project code as well.
# Find_Orb looks through this file from top to bottom. Non-comment
# lines give an observatory code, an optional program code, and a date
# range and magnitude range. (The ranges can be blank, to specify "any
# date" and/or "any magnitude", or to indicate that there is no lower
# or upper limit on that range.) The idea is that such a line defines
# what the sigmas are for any observation from that code, taken within
# that date range, and within that magnitude range.
# When Find_Orb finds a line describing the observation in question,
# it extracts any non-blank sigmas. It keeps going, possibly to
# the bottom of the file, until sigmas have been found for all
# three quantities. That's why there is a final line that will
# assign sigmas to _any_ observation that hasn't already been handled.
# Comments can be added at the end of each line. I've just listed
# the station names in that slot.
# Some comments on how to assign sigmas are at the bottom of this text.
# I've noticed that the following stations get unusually good astrometry.
# These uncertainties roughly reflect how well I've seen them do :
#Obs P <--start-> <--end --> Pos Mag Time
#COD C yyyy mm dd yyyy mm dd mag1 mag2 sig sig sig Comment
689 .1 Flagstaff
673 .1 Table Mountain
422 .3 Loomberah
413 .3 Siding Spring
E12 .25 Siding Spring #2
568 2 .1 .2 David Tholen et. al., Mauna Kea
T09 .1 .2 David Tholen et. al., Subaru
T12 .1 .2 David Tholen et. al., 2.24-m
T14 .1 .2 David Tholen et. al., CFHT
568 ~ .1 .2 TNO survey folks, Mauna Kea
J95 .2 .2 Great Shefford
J75 .2 .1 La Sagra
Y00 .2 SONEAR
# (J95), (Y00) and Tholen at (568) have demonstrated, via observations of
# artsats, that they really have gotten timing right. (J75) has had
# cause to observe very fast-moving artsats; their actual time sigma
# is probably quite a bit better than the above .1 second.
# SOHO and STEREO, though, were not intended to do astrometry and
# produce noisy data. (Each has multiple instruments, and we really
# should take that into account at some point...)
249 10 SOHO
C49 10 STEREO-A
C50 10 STEREO-B
# MPC appears to be weighting (C51) WISE data lightly, which appears to
# be... well... wise:
C51 1 WISE
# ...but Hipparcos and HST get incredibly good astrometry:
248 .01 Hipparcos
250 .01 HST
# The radar folks don't really have 'uncertainties' in RA/dec or mag;
# they aren't measuring those quantities. The quantities they _do_
# measure -- round-trip time and Doppler shift -- have sigmas given
# for them, provided along with the data; we don't need to specify
# them in 'sigma.txt'. The only thing we need to specify is the
# uncertainty in the timing. That sigma really should be effectively
# zero. We can't actually do that, but a nanosecond is good enough.
251 7 1e-9 Arecibo
252 7 1e-9 Goldstone DSS 13, Fort Irwin
253 7 1e-9 Goldstone DSS 13, Fort Irwin
254 7 1e-9 Haystack, Westford
255 7 1e-9 Evpatoria
256 7 1e-9 Green Bank
257 7 1e-9 Goldstone DSS 25, Fort Irwin
259 7 1e-9 EISCAT Tromso UHF
# You MUST have some final "catchall" lines that assign sigmas to all
# observations not otherwise catalogued. Here, we'll say that if the
# observation predates 1993, we'll assume a sigma of 3", no matter
# which observatory it came from. (Older observations are usually
# photographic, and reduced with older catalogues such as the SAO;
# the assumption that they're just a little bit dodgy is usually right.)
1993 01 01 3
# ...which will just leave everything after that date, and we'll
# assume a default sigma for those (more "modern" CCD obs) of a half
# arcsecond, half a magnitude, and one second. This is the "catch-all"
# line mentioned above, to assign uncertainties to anything not already
# found. It's also used if you have turned off weighting (i.e., all
# observations are to be treated equally, with identical uncertainties).
.5 .5 1 Default
# HOW TO ASSIGN SIGMAS: I don't really know of a simple way to do this.
# The above numbers reflect what I've observed in the data, and are
# better than no sigmas at all, but they are somewhat ad hoc.
# One _can_ analyze data from an individual observatory and get a feel
# for what their RMS residuals are and base the sigmas on that. It helps
# if the observatory in question gets a _lot_ of data, to get some
# meaningful statistics. .rwo files give uncertainties assigned in
# this manner.