GPS/MET Glossary

UNDER CONSTRUCTION

4DDA
Four Dimensional Data Assimilation
ACE
attitude control electronics - Unit in Microlab-1 spacecraft that controls spacecraft attitude. Also the suffix of level 0 attitude files.
ACS
Attitude Control System - System, including ACE, sensors, actuators, etc. that are used to sense and control spacecraft attitude.
ancillary
supplementary, auxilliary; see ancillary met
Ancillary Met
Correlative data from other meteorological models and measurements, collected for the purpose of comparison with GPS/MET data. (Also referred to as "correlative data".)
A/S
Anti-Spoofing; a mode that the GPS satellites are usually in, which degrades the accuracy of pseudorange and carrier phase on the L2 signal.
attitude
The Microlab-1 satellite's physical orientation; i.e. which way it's pointing relative to the orbit plane.
attitude mode
refers to any one of several modes the ACE can be set to. Determines the nominal pointing of the spacecraft. See FIXED, INVERSE, and OPTIMUM. (More Information)
azimuth
Angular direction left or right of a reference point or line
BCR
Battery Charge Regulator - electronics unit in the Microlab-1 satellite which controls solar power collection, battery charging, and power distribution.
beta angle
The angle between the plane of the spacecraft's orbit, and the line connecting the centers of the Earth with the Sun. The beta angle partially determines the attitude mode, which in turn governs the amount of power the spacecraft has and the quality of the GPS/MET occultation data. (More Information)
CDDIS
Crustal Dynamics Data Information System
cls
class sonde
colatitude
90 - latitude
double differencing
Data processing technique that combines measurements from four links to elminated all clock and Selective Availability errors.
ecmwf
European Center for Medium Range Weather Forecasting.
elevation
When looking at the sky, "elevation" represents an angle to a satellite up or down from the local horizon.
Ephemeris
A table showing a satellite's location over time.
Extrapolation
In extrapolation mode, the instrument attempts to track occluded satellites, even after it has lost lock on them, by keeping the channel open and trying to catch the signal again.
FAI2
The fiducial site at Fairbanks VLBI Observatory, Alaska
FAIR
The fiducial site at Fairbanks VLBI Observatory, Alaska; combined 30s and 1s measurement system
FC
The Microlab-1 satellite's onboard Flight Computer
FC Reset
Flight Computer Reset -- sometimes the Microlab-1 Flight Computer resets itself, and sometimes it is reset by OSC; in either case it may lead to a gap in GPS/MET data if recovery commands are not sent immediately afterwards.
fid
See Fiducial Site
fiducial
Fiducial sites are fixed GPS receivers on the ground, against which data from the satellite can be differenced. GPS/MET uses data from six sites which take measurements once per second.
FIXED
The "fixed" attitude mode for the Microlab-1 spacecraft refers to periods of time where it attempts to keep the payload's antenna pointed exactly in the anti-velocity direction, which is optimal for the experiment. This is not optimal, however, for the spacecraft's power generation, since it can't yaw back and forth to maximaze the angle at which the sun hits its solar panels. (More Information)
GOL2
The fiducial site in Goldstone VLBI site in California.
GPS
Global Positioning System
GPS/MET
Global Positioning System/Meteorology
haloe
Halogen Occultation Experiment
HR
High Rate occultations, taken at a rate of 50 observations per second; these are used for measurement of the stratosphere and troposphere
HSFE
High Speed Front End - Part of the equipment at the ground station which receives downloaded information
IGS
International GPS Service for Geodynamics; a network of GPS receiver sites, the data from which precise orbits are calculated.
immediate data
When contact is made between the satellite and the ground station to download data, some information regarding the state of the instrument "jumps the queue" and is sent down immediately, ahead of all the scientific data that is waiting to be downloaded.
INVERSE
The "inverse" attitude mode for the Microlab-1 spacecraft refers to the periods of time when the plane of its orbit is more or less edge-on to the sun. In this mode, it yaws back and forth a little, and its solar panels turn, in order to maximize the angle at which the sun hits the solar panels. "INVERSE-180" mode is good for the GPS/MET experiment, because it means the payload's antenna is facing in the anti-velocity direction, so it can observe GPS satellites disappearing over the horizon. (More Information)
KOK2
The fiducial site at Kokee VLBI observatory, Kauai
LAB2
A fiducial site at Jet Propulsion Laboratories
LAB4
A fiducial site at Jet Propulsion Laboratories
latch up
A serious error in the satellite's onboard computer caused by solar radiation.
level 0
Raw data as collected by the orbital equipment, and stored at the POCC
level 1
Data from the satellite and the fiducial sites, grouped by day and put in more manageable files.
level 2
Precise orbits for the Microlab and GPS satellites, and excess phase profiles for each occultation
level 3
Refractivity, bending angle, temperature and pressure profiles for each occultation
lidar
A meteorological measuring system which uses lasers.
load shed
When the spacecraft is short on power or has some other problem, it may turn off the power on the instrument.
LOS
Loss of Signal
LR
Low Rate data; observations taken once every ten seconds, used to calculate the satellite's orbit.
MCM4
The fiducial site at McMurdo Base, Antartica
McMurdo Syndrome
At one point a bug in the instrument's software caused it to act as though the McMurdo base fiducial site was actually in the center of the earth, which affected its choice of occultations to attempt to observe.
megafile
Data file containing both excess phase information and the refractivity, pressure, and temperature profiles derived from them.
met
meteorological
Microlab-1
The satellite containing the GPS/MET instrument.
mls
microwave limb sounder
MR
Medium Rate data; observations taken once per second, used to study the ionosphere.
NCAR
National Center for Atmospheric Research, a division of UCAR
NMC/NCEP
National Meteorological Center / National Center for Environmental Prediction
obscura
Objects on the ground which obscure an earth-based antenna's view.
occultation
Every time the earth comes between the Microlab-1 satellite and a GPS satellite, the GPS satellite appears to be "occluded" or hidden from view. Each time this happens, one set of measurements can be taken, of conditions in the atmosphere at the precise point on the earth's surface where the GPS satellite appears to be setting.
occultation parameters
The software settings on the instrument that govern its choice of occultations to observe. (More Information)
OPTIMUM
The "optimum" attitude mode for the Microlab-1 spacecraft refers to the periods of time when the plane of its orbit is face-on to the sun. This is optimum with regard to power, since the solar panels can continuously face the sun. It's not optimal with respect to the GPS/MET experiment, however, since the spacecraft must face the sun, and the instrument works best when facing in the direction opposite it's velocity. (More Information)
OSC
Orbital Sciences Corporation; the operators of the Microlab-1 satellite.
OSSE
Observing Systems Simulation Experiment -- In this methodology, a weather simulation model is used to generate simulated observations, for input to a separate weather prediction model. The forecast of the prediction model is then compared to the later state of the weather simulation. By using different types of observations to run the prediction model, the usefulness of different observation techniques can be compared.
OTD
Optical Transient Detector: A lightning detection payload which is aboard Microlab-1, along with the GPS/MET instrument.
pitch
Nosing up or down, with respect to direction of motion; see also yaw and roll.
POCC
Payload Operations Control Center -- the computer system in Boulder, CO where the data from the GPS/MET instrument is finally stored, processed, and made available to the public.
POD
Precise Orbit Determination -- The precise location and velocity of the satellite at a given time can be deduced after the fact from GPS measurements made by the satellite and by ground-based IGS stations.
POT2
The fiducial site in Potsdam, Germany
PRN
Pseudo-Random Noise -- one of 32 possible "gold codes" assigned to each GPS satellite; the PRN number is used in this database to identify different GPS satellites.
QC-MET
"Quick Check" software which calculates the approximate angles among the Microlab-1 satellite, the two double-difference GPS satellites, and each of the relevant fiducial sites, for each occultation. This is done immediately after data is received at POCC from the satellite, and is not dependent on precise orbit determination or excess phase calculations.
RAMBO
The software running on the GPS/MET instrument in orbit, which predicts and schedules occultations and stores data from its observations.
RINEX
Receiver Independent Exchange Format; a standard file format for storing the observations of GPS receivers.
roll
Rotation about the axis of motion; see also yaw and pitch
RTS
The antenna system in West Virginia which downloads GPS/MET data from the Microlab-1 satellite approximately every twelve hours.
Rx
receiver
S/A
Selective Availability; a mode that the GPS satellites are usually in, which degrades the accuracy of their signal for non-military users
S/C
Abbreviation for "spacecraft" -- specifically the Microlab-1 satellite
SNR
Signal to Noise Ratio
SOC
state of charge
SOCC
Spacecraft Operations Control Center
SSR
Solid State Recorder -- The Microlab-1 satellite's buffer which stores data until it can be downloaded. The GPS/MET instrument is allocated a segment of the SSR which tends to hold about twelve hours worth of data. When the SSR is full, the instrument overwrites the oldest of its own data.
state vector
A collection of variables that can be uploaded to the satellite to set its state.
SVN
Identification number assigned to each GPS satellite
T1
Telephone company terminology for a specific type of high-bandwidth phone line; in Microlab status reports the term refers specifically to the link between the RTS (where data is downloaded from the satellite) and the SOCC (Spacecraft Operations Control Center).
TID2
The fiducial site at Tidbinbilla Deep space tracking station, Australia
UCAR
University Center for Atmospheric Research
UNAVCO
University Navstar Consortium
yaw
Rotation to the left or right, with respect to direction of motion; see also pitch and roll