| DATA_SET_DESCRIPTION |
Data Set Overview
=================
The REMS instrument is a meteorological suite of sensors designed
to provide measurements of air and ground temperatures, wind speed
and direction, pressure, humidity and ultraviolet radiation.
The REMS MODRDR data set contains processed REMS data converted to
environmental magnitudes and corrected by factors having an
influence in the measurements (such as rover heat sources, shadows
and dust, among others).
The corrections at this level have been applied either by models,
by removing invalid data, or by selecting the most representative
data (e.g. minimum of several sensors). In the case of the Wind
Sensor, modelling includes not only corrections but also the
estimation of the wind data itself. All the original data can be
found in the previous processing levels.
Data is a time ordered sequence of rows organized into a table,
taken at a maximum resolution of one second. Each data product
contains one sol worth of activity and has information from all
sensors.
Like in the ENVRDR there is a confidence level code for each
sensor.
This data set is the highest processing level produced by the REMS
team. It should be of interest to anyone wanting to know Mars
environmental information at the rover's location.
Parameters
==========
This data set includes the following information:
- Wind sensor: horizontal and vertical wind speed, wind direction.
- Ground Temperature Sensor: brightness temperature of thermopile
A (band 8-14 um) and its estimated uncertainty.
- Air Temperature Sensor: local air temperature around each boom
and an estimated ambient temperature around the rover,
calculated after a filtering of both local air temperatures.
- Ultraviolet Sensor: ultraviolet radiation for each band and
their estimated uncertainties.
- Humidity Sensor: local relative humidity, volume mixing ratio,
their estimated calibration uncertainties and the sensor
operating temperature.
- Pressure Sensor: pressure and its uncertainty. Pressure Sensor
configuration (oscillator and low/high resolution mode).
Sampling is at 1Hz maximum, with a baseline operation of 5 minutes
every hour. Additional measurements can be taken on an on-demand
basis beyond those hourly observations. For these additional
measurements, and besides tactical day to day conditions and
resources, there is a general pattern that covers selected hours
of the day built by the scientific team during operations. That
pattern is shifted from sol to sol to cover the whole 24 hours
after a few sols.
Additionally, extended measurements can also be triggered
automatically if event mode is activated, in which case the REMS
computer will decide or not to continue measuring after the
regular cadence, by comparing the previous measurements with the
expected trend. The objective is to capture any ongoing transitory
atmospheric event.
During the first 72 sols, for each 5 minute block, the following
measurement strategy was used: Wind Sensor is switched off for 60
seconds, then it is switched on for 235 seconds, and then it is
switched off again for the final 5 seconds. The rest of the
sensors are switched on all the time. This strategy was based on
results obtained during pre-flight testing. However, after
evaluating flight data, it was determined that this strategy was
not necessary, so from sol 73 onwards all sensors are switched on
for each 5 minute block.
From sol 793 onwards, a new measurement strategy for Humidity
Sensor was introduced. It is called HS HRIM (Humidity Sensor High
Resolution Interval Mode) and is only used on selected one-hour
long observations. This new strategy intends to minimize heating
of the Humidity Sensor, and consists of alternately switching on
and off the sensor at periodic intervals. At the same time, Boom 2
is switched off, which means that there are no Wind Sensor and Air
Temperature Sensor measurements.
Processing
==========
Processing starts with the generation of the REMS EDRs. The REMS
EDR data products are generated by the MIPL (Multimission Image
Processing Laboratory) at JPL, under the OPGS, using the telemetry
processing software called MSLEdrGen. This software will convert
the binary data received from telemetry to ASCII. EDRs will then
be retrieved at Centro de Astrobiologia (INTA-CSIC) using the File
Exchange Interface (FEI).
EDR data products have a first automatic process using calibration
data. The result of this is the TELRDR data set, which contains
electrical magnitudes and thermal data. In parallel, using
ancillary data provided by JPL (such as rover location, sun
position) the ADRs (Ancillary Data Records) are generated. EDRs,
TELRDRs, ADRs, and calibration data are processed together to
obtain the ENVRDRs.
The level of processing of the ENVRDRs includes environmental
magnitudes with minimal corrections (mainly based on the
degradation of the sensors). Finally, applying models developed by
the REMS team and refining them with the confidence levels, the
MODRDR data set is created.
The processing to be applied to convert ENVRDR to MODRDR is the
following:
- Wind Sensor: application of an inverse model (based on
calibration tests on a wind tunnel) to convert differential
thermal conductances to wind speed and direction. Data too
noisy, data taken with voltage out of range, and data taken with
a gain not fully characterized is removed.
- Ground Temperature Sensor: removed data from thermopiles B and C
since their uncertainty is too high. Removed data not in
calibration sequence or acquired when ASIC temperature is unstable.
- Air Temperature Sensor: application of a model to get the local
air temperature around each boom, by using the individual PT1000
sensors temperatures. Afterwards, a a single air temperature is
calculated by filtering those two local air temperatures.
- Ultraviolet Sensor: removed data measured when SZA (Solar
Zenith Angle) is in a range which causes internal reflections inside
the photodiodes. Data measured when the rover or the arm were
moving is also removed.
- Humidity Sensor: the median of the three humidity channels is
calculated to get the local relative humidity. Volume Mixing
Ratio is also calculated.
- Pressure Sensor: data with drift correction applied.
ADRs are used mainly to populate the confidence level codes found
in MODRDRs. Some of those confidence levels take into account the
projection of the shadows over the sensors using positions and
locations contained in the ADRs.
Finally, with a one to one time match between ENVRDR and MODRDR,
the resulting data is integrated into a single table.
Data
====
Each REMS MODRDR product in the data set is an ASCII table
containing all sensors data. Each row contains an acquisition
session, and columns contain the sensors values.
Columns with related information are placed together, in the
following order: time references (REMS clock, LMST and LTST), Wind
Sensor, Ground Temperature Sensor, Air Temperature Sensor,
Ultraviolet Sensor, Humidity Sensor and Pressure Sensor.
REMS clock is synced with the spacecraft clock (SCLK) with a
maximum deviation of 30 sg. LTST is given with respect to the
rover position, in contrast with LTST given in REMS EDR labels and
in other MSL data, which is given with respect to landing site.
A confidence level code for each sensor is included. This code
indicates the quality of the data by a string of zeroes and ones.
Each character represents a factor by a '1' (good condition) or a
'0' (bad condition). The higher the number of ones, the more
reliable the measured magnitude is. The character 'X' may be
present in some codes for factors whose value is not known at the
moment of the data generation. A detailed description of the
confidence levels can be found in the REMS RDR SIS.
In addition to confidence level codes, some sensors include an
estimation of the uncertainty in the provided data in another
column.
Columns are delimited by commas and are of fixed length. Rows are
time ordered and are separated by a carriage return/line
feed. Each table contains a sol of measurements.
Data may be set to UNK if their value is not known and it will
never be (such as saturation, or a specific sensor switched off
during acquisition). They may also be set to NULL if their value
is not known at the moment of the release of the data set, but it
is expected to be known in a future release. If data from a sensor
is set to UNK or NULL, its associated confidence level code will
also be set to UNK or NULL.
Ancillary Data
==============
The ancillary data used in the generation of MODRDR data are
laboratory calibration data and ADRs.
Calibration data can be found in the CALIB directory. Calibration
files are in plain ASCII text format. They are structured in a PDS
label-like structure, with the form DATA = VALUE, each value
taking up one line. A file per sensor is provided.
The following information is contained in the ADRs:
Solar azimuth and elevation
Rover azimuth, elevation, altitude, pitch, yaw and roll
Rover speed
Masthead azimuth and elevation
Rover temperatures
UV sensor dust attenuation
Coordinate System
=================
This data set depends on several coordinate systems used in the MSL
project. These are:
- MSL_TOPO frame, fixed to landing site, is used to define rover
position.
- MSL_LOCAL_LEVEL, fixed to the rover, is used to define rover
orientation (roll, pitch and yaw angles)
- MSL_RSM_ZERO_AZ frame, fixed to the rover, is used to define
rover remote sensor mast (RSM) azimuth.
- MSL_RSM_ZERO_EL, fixed to the rover, is used to define rover
remote sensor mast (RSM) elevation.
- MSL_ROVER_MECH, fixed to the rover, is used to define Sun
position angles (azimuth and elevation)
Software
========
No software is provided in this data set. The RDR tables are simple
ASCII files that can be displayed on UNIX, Macintosh, and PC
platforms with common software.
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