REMS_DESCRIPTION.txt

PDS_VERSION_ID        = PDS3
LABEL_REVISION_NOTE   = "2011-04-05, REMS TEAM, initial;
                         2013-01-26, lmora, updates, added references;"
RECORD_TYPE           = STREAM

OBJECT     = INSTRUMENT
  INSTRUMENT_HOST_ID = MSL
  INSTRUMENT_ID      = REMS

  OBJECT     = INSTRUMENT_INFORMATION
    INSTRUMENT_NAME = "ROVER ENVIRONMENTAL MONITORING STATION"
    INSTRUMENT_TYPE = "ENVIRONMENTAL_STATION"
    INSTRUMENT_DESC = "


  Instrument Overview
  ===================
    The Rover Environmental Monitoring Station (REMS) instrument is
    intended to provide in situ near-surface measurements of air and
    ground temperatures, wind speed and direction, pressure, humidity
    and ultraviolet radiation. Its objective is to characterize the
    Martian climate and to study Mars habitability.

    Systematic measurement is the main driver for REMS operation. Each
    hour, every sol, REMS will record 5 minutes of data at 1 Hz for
    all sensors. This strategy will be implemented based on a high
    degree of autonomy in REMS operations. The instrument will wake
    itself up each hour and after recording and storing data, will go
    to sleep independently of rover operations. REMS will record data
    whether the rover is awake or not, and both day and night. 

    REMS operation is designed assuming a minimum of three hours of
    operation each day, primarily constrained by power
    availability. Since the hourly observations will use a total of
    two hours of operational time, the third hour can be scheduled as
    a continuous block, for example. Another option that has been
    implemented in REMS flight software is a simple algorithm to
    lengthen some of the regular observations autonomously when an
    atmospheric event is detected. Depending on resources available
    during the mission, and the science team wishes, REMS can operate
    more than three hours per day.

    REMS instrument is formed by four main subsets: 

    - ICU (instrument Control Unit), allowing power conditioning and
      distribution, analog acquisition and control of some of the
      sensor, thermal control loops, communications with the Booms and
      data processing and communications with the RCE. The ICU is
      composed of three boards: CPU, Analog and a DC/DC Converter. The
      Analog board also integrates the Pressure Sensor (PS).

    - Ultraviolet Sensor (UV), consisting of 6 photodiodes, each one
      devoted to a different measurement band.

    - Boom 1, hosting an Air Temperature Sensor (ATS), a Wind Sensor
      (WS), the Ground Temperature Sensor (GTS) and the front-end ASIC
      that processes all the received analog inputs from the
      transducers and sends the data to the ICU via a transmission
      link.

    - Boom 2, hosting another Air Temperature Sensor, another Wind
      Sensor, the Humidity Sensor (HS) and other front-end ASIC that
      also processes all the received analog inputs from the
      transducers and sends the data to the ICU via a transmission
      link.

    Booms are to be located orthogonal to the rover mast, with boom 1
    looking to the side and slightly to the rear of the rover, while
    boom 2 points in the driving direction of the rover. The UVS is
    going to be placed on top of the Rover Deck and the ICU is to be
    located inside the warm body of the rover.  

    An extensive description of the REMS instrument can be found in
    [GOMEZELVIRAETAL2012].

  Scientific Objectives
  =====================
    The five main science objectives of REMS are:

    1) Microscale atmospheric Dynamics. Characterization of the
       near-surface meteorological environment at Diurnal and Seasonal
       Scales.

    2) Mesoscale atmospheric Dynamics. It includes flows forced by
       interaction of solar heating and large-scale winds with
       topography or other surface inhomogeneity such as sharp
       contrast in surface inhomogeneity (10-1000 km).

    3) Synoptic atmospheric Dynamics. A fundamental scientific
       objective is the characterization of the atmospheric global
       waves (> 1000 km) through the pressure fluctuations records.

    4) The Local Water Cycle. The fluctuations of the diurnal water
       vapour concentration will increase our knowledge about the Mars
       water cycle at the boundary layer.

    5) The Local UV Environment at the surface. To evaluate the role
       of the UV radiation environment in the local chemical and
       biological processes.


  Calibration
  ===========
   The Calibration for the REMS instrument is provided in the REMS
   Calibration Plan (DOCUMENT/REMS_CALIB_PLAN.PDF of this volume).


  Operational Considerations
  ==========================

    Boom Thermal Management
    ----------------------
      Mixed ASIC inside each Boom needs to be warmed-up to
      temperatures over -55C before they are used.  This is performed
      automatically be a hardware (software-assisted) control-loop
      implemented into the ICU for any operation that requires Booms
      ASIC use (science data acquisition, engineering acquisition,
      ground temperature sensor calibration).
  
      When the Booms ambient temperature is too low, the ICU will
      switch-on the Booms' ASIC heater at temperatures below
      approx. -54C nominally. On reaching -70C (this is a default but
      modifiable parameter) the ASICs will be switched on and start
      operation. The heater will be switched-off when the temperature
      reaches approx -50C nominally.
    
      Any operation requiring Booms operation will be automatically
      delayed until the Booms reaches operation temperatures. This is
      performed automatically by instrument and need just to be taken
      into account in the operations planning.  The ICU includes a 15
      minutes warming-up timeout. In case one ASIC does not reach
      operation temperature before that timeout expires the ASIC is
      declared failed and the operation continues with the other
      available sensors.

    Sensors management
    ------------------  
      It is occasionally necessary to perform sensors management
      procedures to allow correct operation and to improve the
      performance of the sensors (e.g. by obtaining calibration data).
    
      Three sensor management operations are presently defined: HS
      regeneration, HS defrosting and GTS calibration.
    
      HS Regeneration shall be done about once a month by ground
      command when the ambient temperature is at its highest. Nominal
      regeneration time target is between 3 and 10 minutes, being this
      time a changeable parameter (via a System
      Parameter). Regeneration temperature target is between +135C and
      150C.  This restores Humicap calibration by removing
      contamination from the sensor surface.
    
      HS regeneration is performed by sending the corresponding
      Instrument Command or by setting the equivalent entry into the
      Schedule Table when operating in Auto mode.  Please note that
      REMS software includes an enabling ambient temperature window
      array that will be checked automatically by the software before
      proceeding with the regeneration. Regeneration will then only be
      performed if the ambient temperature as measured by the own HS
      channel is between the upper and lower limits programmed in such
      table (as System Parameters).
    
      HS Defrosting procedure is similar to the regeneration one. It
      requires no more than +100C as H-PRT temperature, thus removing
      frost in the sensor heads. Defrosting shall be done every night
      at coldest night hours (ambient temperature usually below -50C,
      but depends on ICU H-PRT secondary voltage level at that time)
      by pre-defined timeline commanding or by direct ground
      command. Nominal defrosting time is between 3 and 5 minutes, but
      this time shall be a changeable by a System Parameter.
        
      HS Defrosting is performed by sending the corresponding I-cmd or
      by setting the equivalent entry into the Schedule Table when
      operating in Auto mode.  As with the regeneration, REMS software
      includes an enabling ambient temperature window array that will
      be checked automatically by the software before proceeding with
      the defrosting. Defrosting will only be performed in case the
      ambient temperature as measured by the own HS channel is inside
      the upper and lower limits programmed in such table (as System
      Parameters).
    
      Humidity Sensor should be calibrated at night, when the
      temperature is so low that the humidity reaches its saturation
      level. Data for calibration will be taken through a standard
      measurement cycle, not requiring any specific sensor operation.
    
      For calibration of the GTS sensor thermopiles, a heater placed
      in front of the thermopiles is implemented (intercepting part of
      the thermopiles field of view) and heated to a known power
      (~330mW, typical) during the calibration mode of the
      instrument. In this way, it will provide a thermal gradient of
      at least 30C between the calibration plate and the thermopiles
      reference temperature, thus giving a good thermopile output
      response. This operation should be performed when ambient
      temperatures are as stable as possible (and consequently, there
      are calm winds), to minimize error contributions.


  Detectors                                                               
  =========           
    Wind speed and direction will be derived based on information
    provided by three two-dimensional wind sensors on each of the
    booms. The basic concepts in which the two-dimensional wind
    sensors are based can be found in [DOMINGUEZETAL2009]. The three
    sensors are located 120 degrees apart around the boom axis. Each
    of them will record local speed and direction in the plane of the
    sensor. The convolution of the 12 data points will be enough to
    determine wind speed as well as pitch and yaw angle of each boom
    relative to the flow direction. The requirement is to determine
    horizontal wind speed with 1 m/sec accuracy in the range of 0 to
    70 m/sec, with a resolution of 0.5 m/sec. The directional accuracy
    is expected to be better than 30 degrees. For vertical wind the
    range is 0 to 10 m/sec, and the accuracy and resolution are the
    same as for horizontal wind.

    Ground temperature will be recorded with a thermopile on Boom 1
    that views the Martian surface to the side of the rover through a
    filter with a passband of 8 to 14 microns. The requirement is to
    measure ground brightness temperature over the range from 150 to
    300 K with a resolution of 2 K and an accuracy of 10 K.  Please
    see [SEBASTIANETAL2010] for a further information about the GTS
    sensor.

    Air temperature will be recorded at both booms with two
    PT1000-type sensors placed on a small rod long enough to be
    outside the mast and boom thermal boundary layers. The information
    provided by these two sensors alongside knowledge of the
    temperature at the base of the rod (boom temperature) shall be
    used to estimate the temperature of the fluid around it.  Its
    measurement range is 150 to 300 K. It has an accuracy of 5 K and a
    resolution of 0.1 K.

    Boom 2 houses the humidity sensor, which is located inside a
    protective cylinder. That sensor will measure relative humidity
    with an accuracy of 10% in the 200-323 K range and with a
    resolution of 1%. A dust filter protects it from dust deposition.

    The UV sensor will be located on the rover deck and is composed of
    six photodiodes in the following ranges: 315-370 nm (UVA), 280-320
    nm (UVB), 220-280 nm (UVC), 200-370 nm (total dose), 230-290 nm
    (UVD), and 300-350 nm (UVE), with an accuracy better than 8% of
    the full range for each channel, computed based on Mars radiation
    levels and minimum dust opacity. The photodiodes face the zenith
    direction and have a field of view of 60 degrees. The sensor will
    be placed on the rover deck without any dust protection. To
    mitigate dust degradation, a magnetic ring has been placed around
    each photodiode with the aim of maximizing their operational
    time. Nevertheless, to evaluate dust deposition degradation,
    images of the sensor will be recorded periodically. Comparison of
    these images with laboratory measurements will permit evaluation
    of the level of dust absorption.

    The pressure sensor will be located inside the rover body and
    connected to the external atmosphere via a tube. The tube exits
    the rover body through a small opening with protection against
    dust deposition. Its measurement range goes from 1 to 1150 Pa with
    an end-of-life accuracy of 20 Pa (calibration tests give values
    around 3 Pa) and a resolution of 0.5 Pa. As this component will be
    in contact with the atmosphere, a HEPA filter will be placed on
    the tube inlet to avoid contaminating the Mars environment.

    More information about each sensor can also be found in the REMS
    Calibration Plan.

  Electronics
  ===========
    REMS electronics consist of the ICU and the ASICs on both
    booms. The intra-instrument harness connecting these elements is
    provided by JPL.

    The development of an ASIC for data conditioning is motivated by
    two requirements: the need for the booms to survive and operate in
    a broad range of temperatures, and for the entire instrument to
    have a mass less than 1.3 kg. The ASIC must survive a -130C to
    +70C temperature range and minimize power consumption for
    operation.

    The Booms' sensors signals (exception made of the Humidity Sensor)
    are acquired through the Mixed Analog/Digital ASIC, which are
    accommodated inside the booms housing. These ASICs communicates
    via serial links with the Instrument Control Unit down in the
    Rover warm body. There will be a master-slave communication
    protocol, being the ICU the master of the communications; ICU will
    sent commands to the ASICs and wait for reply from them (ASICs
    cannot initiate communications), There will be always an answer
    for every command sent. In addition, the ICU can not send a
    command while a previous answer is pending. Humidity Sensor's
    signals (Boom 2) are directly connected -via harness- to the ICU
    for its control and data acquisition.

    On board software runs inside the ICU microprocessor. There are
    two on-board REMS software products:

    - Start Up SW (SUSW): Stored in PROM, it can not be changed during
      the mission. This product will be in charge of the booting
      tasks, initial instrument initialization/testing and patching of
      APSW. SUSW will start the execution of APSW.

    - Application SW (APSW): Stored in EEPROM, it may be changed
      during the mission. This product will perform the instrument
      management operations and the scientific data
      acquisition/downloading. EEPROM contains also a Memory
      Management Parameters are (MMP) that defines important software
      configuration parameters such as base pointers and sizes of
      Application Software, REMS Data Product buffer, Schedule Table,
      System parameters area, etc.

    Science and Engineering data is stored into a Flash EEPROM (as
    RDP_Data_Product) to be later on downloaded for telemetry. This
    Flash Memory is used to store non volatile data structures that
    need to be kept through REMS sleep/wake cycles but at the same
    time they need to be often read/modified by REMS SUSW and APSW
    during nominal operation.

    The following data structures are stored in the Flash memory: 

    - Schedule Table, contains the specification of tasks to be done in
      APSW Auto mode. This table needs to be loaded periodically into the
      instrument.

    - REMS Data Product, scientific and operational data gathered by the
      instrument. This data has to be downloaded periodically.  

    - System Parameters (SP), persistent but modifiable information needed
      for nominal instrument operation (e.g. Booms' ASICs default power-on
      configurations, sensors gains, sensors management limits and
      operational durations, Event mode parameters, etc.  

    - Persistent data, SW internal variables that need to be kept
      between resets, for example ST and RDP management information
      (e.g. internal pointers to flash structures, measurements
      averages for Event mode calculations, OBT value before going to
      standby, etc.). The allocation and sizes for these structures
      are specified inside the MMP stored in EEPROM.

  Operational Modes
  =================
    REMS can operate either: 

    - Autonomously, in base of a given 'Schedule Table' that is uploaded
      to the instrument,

    - Or supervised, by means of Instrument commands (I-cmds) sent
      directly from the rover. This will be used mainly to load the
      Schedule Table or to handle special situations.

    The baseline operations scheme has the instrument waking up every
    hour to take 5 minutes of observations, with each sensor
    collecting samples at 1 Hz. This scheme will provide 2 hours of
    data per sol, and will be implemented using the Schedule Table.

    In addition to the baseline hourly observation cadence, REMS can
    operate continuously for longer periods, be either in one single
    block or into several smaller blocks distributed along the sol. It
    is foreseen a total extra time of one hour each day, but can be
    more depending on mission resources and the wishes of the science
    team.

    The additional observations can be handled in several ways. One is
    by examining phenomena of known interest (e.g. atmospheric
    conditions at dawn or dusk). Other one is by distributing several
    observations along each sol and then shifting them the following
    sols. That way, after several days, a full 24 hour cycle of
    measurements can been covered.
 
    There is also the possibility of using the extra observation time
    by activating the REMS event mode. In that mode, REMS will make
    real time comparisons between data taken during the hourly 5
    minutes periods and an expected trend kept in memory. These
    comparisons may trigger additional observations (up to a
    predefined maximum) immediately following the scheduled hourly
    periods. These triggers are based on observations statistics, such
    as absolute values or unusual temporal variations, and try to
    detect any ongoing transitory atmospheric event."

  END_OBJECT         = INSTRUMENT_INFORMATION

  OBJECT             = INSTRUMENT_REFERENCE_INFO
    REFERENCE_KEY_ID = "GOMEZELVIRAETAL2012"
  END_OBJECT         = INSTRUMENT_REFERENCE_INFO

  OBJECT             = INSTRUMENT_REFERENCE_INFO
    REFERENCE_KEY_ID = "SEBASTIANETAL2010"
  END_OBJECT         = INSTRUMENT_REFERENCE_INFO

  OBJECT             = INSTRUMENT_REFERENCE_INFO
    REFERENCE_KEY_ID = "DOMINGUEZETAL2009"
  END_OBJECT         = INSTRUMENT_REFERENCE_INFO

END_OBJECT           = INSTRUMENT

END