| DATA_SET_DESCRIPTION |
Data Set Overview
=================
The Microscopy, Electrochemistry, and Conductivity Analyzer (MECA)
experiment on the Mars Phoenix Lander consists of four instrument
components plus command electronics. This MECA Non-Imaging Reduced
data set contains data from three of the four MECA components, the
Thermal and Electrical Conductivity Probe (TECP), the Atomic Force
Microscope (AFM), and the Wet Chemistry Laboratory (WCL).
Reduced data from the fourth MECA component, the Optical Microscope
(OM), is in a separate data set.
More information is found in HECHTETAL2008, KOUNAVESETAL2008, and
ZENTETAL2008.
The following text describes each component of the data set.
TECP Overview
=============
An end-effector on the Phoenix Robotic Arm, the Thermal and
Electrical Conductivity Probe (TECP) is a probe
of soil physical properties including temperature, thermal
conductivity and diffusivity, electrical conductivity and
permittivity, as well as atmospheric temperature, humidity, and
wind speed. These measurements are made with four conical needles,
three of which contain electrical heaters and thermometers, and
a hygrometer sensor mounted separately in the body of the TECP.
The scientific objectives of the TECP are to provide ground-truth
for orbital surface thermal measurements and input parameters for
thermal models by directly measuring the thermal properties of
Martian regolith; to measure the concentration and nature of water
in Martian regolith in solid, 'non-frozen,' liquid, and vapor
states; to determine changes in the reservoirs of water when soil
is freshly exposed and; to characterize the movement of water in
and out of the soil by measuring atmospheric humidity,
temperature, and wind speed above the surface.
The MECA TECP portion of the PHOENIX MARS MECA NON-IMAGING RDR
V1.0 data set is a collection of electrical conductivity (EC),
relative humidity (HUM), relative permittivity (PRM), and
thermocouple (needle) temperature (TC) data sorted by time. Data
are sorted by time, with each data file containing one one sol's
worth of data for each data type.
TECP Parameters
===============
Spatial parameters are given for each TECP sample in the RDR data
set. These parameters allow the end-user to determine the exact
position of the TECP during each data collection. The coordinates
are given in several reference frames that are discussed in the
Coordinate System section of this document.
TIP_POS_R_PF - Radial coordinate of TECP needle tips centroid in
Payload Frame cylindrical coordinates
TIP_POS_THETA_PF - Azimuthal coordinate of TECP needle tips
centroid in Payload Frame cylindrical
coordinates, measured clockwise
(as viewed from above) from the +x-axis
TIP_POS_Z_PF - Vertical coordinate of TECP needle tips centroid
in Payload Frame cylindrical coordinates, measured
positive downward
ANGLE_TECP_RA - Angle of TECP long axis (+z axis in TECP frame)
relative to a vector that is parallel to the RA
forearm and pointing away from the lander.
This angle is measured clockwise as viewed from
the TECP side of the RA wrist joint.
TIP_POS_X_LLF - X coordinate of the TECP needle tips centroid in
the Local Level Frame
TIP_POS_Y_LLF - Y coordinate of the TECP needle tips centroid in
the Local Level Frame
TIP_POS_Z_LLF - Z coordinate of the TECP needle tips centroid in
the Local Level Frame, measured positive downward
ANGLE_TECP_Z_LLF - Angle of TECP long axis (+z axis in TECP frame)
relative to the positive z-axis of the Local
Level Frame (parallel to gravity vector)
TECP Processing
===============
There are four types of TECP data, electrical conductivity
(designated EC), humidity (designated HUM), relative permittivity
or dielectric constant (designated PRM) and temperature (TC). The
EC data is formatted as four ASCII tables, a conversions table,
two tables with conversion constants, and a data table that
contains a time-series of measurements. The HUM, PRM and TC data
are all formatted as a conversions table followed by a data table
that contains a time-series of measurements. The conversions table
contains the DN to physical unit equations for the particular data
type. Table 4.5 of the MECA RDR SIS found in the DOCUMENTS
directory of this archive lists all the DN to physical unit
conversions used to convert TECP EDR data into TECP RDR data.
TECP Data
=========
There are four types of TECP data, TECP_EC, TECP_HUM, TECP_PRM
and TECP_TC. The TECP_EC data is a time-series of electrical
conductivity measurements. The TECP_HUM data is a time-series of
relative humidity measurements. The TECP_PRM data is a time-series
of relative permittivity data, and the TECP_TC data is a
time-series of temperature measurements. The TECP data are
organized as ASCII CSV data files. The TECP_EC data files are
structured as a 2-column conversions table that holds the DN to
physical unit conversion equations. The conversions table is
followed by a 4-column table that holds the gain specific probe
constant conversion coefficients. Next is a 7-column table that
contains the gain specific resistance conversion coefficients and
last the 13-column data table. The TECP_HUM, TECP_PRM, and TECP_TC
data files are all structured in the same way. The file begins
with a 2-column conversions table that holds the DN to physical
unit conversions used to make the RDRs. The conversions table is
followed by the data table. The EC and HUM data are 13-column data
tables. The PRM data table is a 12-column data table and the TC
data table is a 16-column table.
Each of the four TECP data types are organized as ASCII comma
separated variable (CSV) data files containing data from a single
Martian sol, with a detached ASCII text PDS label file for each
data file. Data from each measurement day will be grouped by
instrument (TECP) then by sol.
TECP Ancillary Data
===================
The first table in all the TECP RDR data types is a conversions
table. This table gives the DN to physical unit conversion
equations used to convert the raw TECP EDR DN value data to
physical units. The EC data type also contains a table of
calibration coefficients used in the EC conversions. It is
possible that these coefficients could change over the course
of the mission. If they do change, the change will be noted in
this document, as well as in the RDR SIS.
TECP Coordinate System
======================
TECP orientation information is given in all four TECP data types.
The orientation information is obtained from the Robotic Arm (RA)
and was acquired at the time of the most recent RA move. The
orientation information is given in both the payload frame and in
the local level frame for ease of use. The definitions of the
PHOENIX coordinate systems are documented below:
Local Level - Same as payload frame, and it moves with the Lander
+X - North
+Z - down along gravity vector
+Y - East
Payload Frame - At the shoulder of the Robotic Arm. Attached and
moves with the Lander
+X - along Lander X (point out into the work
space)
+Z - down along Lander (vertical axis)
+Y - along Lander -Y
Site Frame - Same as payload frame when first defined and never
moves relative to Mars. Possible to define multiple
site frames in case the Lander moves/slips.
Same as local level
TECP Software
=============
No TECP specific software will be provided at this time. As the
data products are ASCII, any software that can handle ASCII files
can be used to view the products.
TECP Media/Format
=================
As part of the MECA Non-Imaging RDR data set, TECP RDRs will be
delivered using Internet file transfer
protocol. Data formats will be based on standards for such
products established by the Planetary Data System (PDS)
[PDSSR2001].
AFM Overview
============
The Atomic Force Microscope (AFM) is part of the MECA Microscopy
Station, which comprises a Sample Wheel and Translation Stage
(SWTS), an optical microscope (OM), and the AFM. The MECA AFM is
located between the OM and the SWTS inside the darkened MECA
enclosure on the spacecraft deck. It scans a small region
(from 1-65 micron square) on any of 69 substrates, each 3-mm in
diameter, positioned along the rim of the SWTS. The chief
scientific objectives of the AFM are to analyze small dust and
soil particles in terms of their size, size distribution, shape,
and texture. The AFM is particularly well suited to analyze
particles carried by the wind, which are believed to be in the
size range 1-3 micron. A full description of the MECA AFM can be
found in [HECHTETAL2008].
The MECA AFM portion of the PHOENIX MARS MECA NON-IMAGING RDR V1.0
data set is a collection of scan data sorted by time. Data types
included in this data set are the AFM_SDR, calibrated scan data
with x-y scan ranges, the AFM_SDD, a line by line derivative of
the calibrated scan data, and the AFM_REPORT, a daily description
of AFM mission activities. Data are sorted by time, with each data
folder containing one sol's worth of data for each data type.
The two scan data AFM RDR data products are formatted to have a
detached ASCII PDS label. The SDR and SDD data products consist of
five attached data tables. The first table is the header table
that describes the AFM scan parameters and other important
information pertaining to that scan, followed by the
calibrated scan data in four sequential ASCII TABLE objects.
AFM Parameters
==============
The AFM scan parameters of interest for each scan are captured in
the AFM_HEADER_TABLE, which is found at the beginning of the scan
data. The following is a list of the header parameters.
cmdTimewhole - Spacecraft command receipt time (whole seconds)
cmdTimeremainder - Spacecraft command receipt time (remainder)
readTimewhole - Time at which last scanline was received from the
instrument
readTimeremainder - Time at which last scanline was received from
the instrument (remainder)
dataLength - Record length (minus headers) Bytes
Cols - Image width Points
Lines - Image height Lines
Direction - Scan direction mask. 1 = forward, 2 = backward
Channel - 1 = error, 2 = height.
channelGain - Determines the topographic height scale, Ranges
from 0 to 8, with 0=full range (13.8 microns), and
reducing by factors of 2 each time. i.e.
Gain of 2 = 3.45 microns.
refOMimage - Filename of the relevant OM image taken at the AFM
scan position prior to start of the scan. This
provides the context for interpreting the AFM scan
data.
opsToken - Ops token
SwtsTemperature - Temperature of the SWTS just prior to the scan
Scanrange - Scan range of slow and fast scan axes
Height_scaling_factor - The scaling factor used to calibrate the
height data (converts DNs to micrometers)
Smoothing_factor - Number of points used in the Savitzky-Golay
filter function. (for SDD only)
AFM_OM_ref_x - The approximate location of the center of the AFM
scan field relative to the OM image. X-coordinate
in pixels.
AFM_OM_ref_y - The approximate location of the center of the AFM
scan field relative to the OM image. Y-coordinate
in pixels.
X-slope - The x-slope of the sub-strait relative to the x-y
scanner.
Y_slope - The y-slope of the sub-strait relative to the x-y
scanner.
AFM Processing
==============
The AFM_SDR data type is calibrated scan data with x-y scan
ranges. The height and scan range data will be calibrated
based on data from calibration scans of the AFM pincushion
substrate that will be performed just prior to the AFM scans
on Mars. The scaling factor used for the conversion from DNs to
micrometers will be included in the header of the RDR. Data are
presented in units of micrometers and represented by real numbers
to three decimal places. The error channel data in this data type
are given in units of Volts with no in-situ calibration applied
and represented by real numbers to six decimal places.
The AFM_SDD data type is a line by line derivative of the
calibrated scan data. By converting slope to grayscale,
derivatives are a simple way to simulate what the eye would see if
the topographs represented macroscopic surfaces illuminated from
overhead. The derivative will be performed using the
Savitsky-Golav method, following the raster-scanning direction
because the discontinuities that are often present between lines
would produce unacceptable noise in a true 2-dimensional
derivative.
Savitzky-Golay is a simple running filter that smoothes data while
optionally performing various orders of derivatives, depending on
the selection of filter parameters. It is equivalent to performing
a local polynomial regression of degree k on at least k+1
equally-spaced points. For the AFM derivatives, selection of the
number of points will be done manually depending on the noisiness
of the data. The number of points used is recorded in the
derivative header table in the smoothing_factor field.
AFM Data
========
There are three AFM data types, the AFM_SDR, the AFM_SDD and the
AFM REPORT. The AFM_SDR is the converted scan data record and the
AFM_SDD is the scan data derivative. The first two data types are
structured as five table units (files) that contain a 20 or
21-column 4-row header table, a 1536-column forward scan error
table, a 1536-column forward scan height data table, a 1536-column
backward scan error table, and a 1536-column backward scan height
table. The AFM REPORT is a text file that describes the activities
of a measurement day. See Appendix D for label examples and table
structures.
The AFM_SDR and AFM_SDD are organized as ASCII comma separated
variable (CSV) data files containing data from a single scan of
the AFM, with a detached ASCII text PDS label file for each data
file. The AFM REPORT is an ASCII text file with an attached ASCII
PDS label. Data from each measurement day will be grouped by
instrument (AFM) and then by sol.
AFM Ancillary Data
==================
The AFM REPORT data type is ancillary data that explains the daily
operations of the AFM. This is an ASCII text file with an attached
PDS label that contains a narrative of events during an
operational day. There will be one file per sol that is manually
generated by an AFM team member. This file may contain items such
as rationalemfor picking a particular target, difficulties in
making a particular measurement, or other general information that
is not easily captured elsewhere.
AFM Coordinate System
=====================
The AFM scan plane is a square that is rotated clockwise by
45-degrees and flipped vertically relative to an OM image. The
axis that defines a scan line (the one along which scan samples
are taken) is called the fast-axis (i.e. it increments/decrements
more rapidly). The other axis determines scan line rows and is
only incremented/decremented at the end of each scan line. Thus it
is referred to as the slow-axis. The default fast-axis for the AFM
is the x-axis, the default slow axis is the y-axis. Note that the
scan point (0,0) is in the middle of the scan plane, i.e. for a
256 x 256 scan, the scan field goes from -127 to +127 in x and
-127 and +127 in y. The starting point of a scan is not the origin
of the scan field however, but the most negative x and y
positions, i.e. for a 256 x 256 scan, the scan starts at the point
(x=-127,y=-127) and proceeds to more positive values in both
directions.
The scan data is ordered such that the first line of data in the
file represents the first line of data acquired by the AFM. The
AFM acquires the scan data in an 'upward' (or positive 'y')
direction in the AFM scan coordinate system. However, as described
above and shown in Figure 4 1, the AFM coordinate system is
flipped and rotated relative to the OM coordinate system. Thus,
plotting the data in the order that it is shown in the file
produces an 'upside down' image relative to the MECA-OM image.
AFM Software
============
No AFM specific software will be provided at this time. As the
data products are ASCII, any software that can handle ASCII files
can be used to view the products.
AFM Media/Format
================
As part of the MECA Non-Imaging RDR data set, AFM RDRs will be
delivered using Internet file transfer
protocol. Data formats will be based on standards for such
products established by the Planetary Data System (PDS)
[PDSSR2001].
WCL Overview
============
MECA's wet chemistry laboratory (WCL) comprises four single-use
modules, each consisting of a beaker assembly and an actuator
assembly. The modules mix soil samples with a leaching solution
in a pressure vessel for electrochemical analysis. The scientific
objective of the WCL is to determine the total pH, redox
properties, and concentration of the principal aqueously solvated
components of the acquired soil samples.
Chemical data is returned by 26 distinct sensors, some redundant,
lining the walls of each beaker. These measure: Temperature;
pH (3); conductivity; oxidation-reduction potential; the anions
chloride (2), bromide, and iodide; cations sodium, potassium,
calcium, magnesium; and barium, used in a sulfate titration. Also
included are electrodes for cyclic voltammetry, anodic stripping
voltammetry, and chronopotentiometry (3). Lithium electrodes (2)
are used as a reference relative to the known concentration of
lithium salts in the solution. Sensors for nitrate, ammonium,
dissolved oxygen and carbon dioxide, which for various reasons do
not provide a quantitative measure of soil composition, are used
only for context. A heater is imbedded in the base of the beaker
to maintain water temperature during operation. A full description
of the MECA WCL can be found in [KOUNAVESETAL2008].
The MECA WCL portion of the PHOENIX MARS MECA NON-IMAGING RDR V1.0
data set is a collection of chemical data, conductivity, cyclic
voltammetry, chronopotentiometry, and pressure and temperature data
that is sorted by time. Data types included in this data set are:
ISE - Ion-Selective electrode data,
CND - conductivity data,
CV - Cyclic voltammetry data,
CP - Chronopotentiometry data,
PT - Pressure and temperature data.
Data are sorted by data type and by time, with each data folder
containing one sol's worth of data for each data type.
WCL Parameters
==============
Important measurement parameters are recorded in the header table
found at the beginning of each of the RDRs. The header tables for
the ISE, CND, and PT data types are identical, and contain the
following parameters:
PRODUCT_TYPE - The product type, MECA_WCL_CND
PLANET_DAY_NUMBER - Mission Sol number on which the data
was acquired
PLANET_DAY_TYPE - The measurement day type. A = first
day of measurements on a sample,
B = second day of measurements on a
sample. O = other.
WCL_CELL - The number of the WCL cell(0-3)
PARENT_EDR - The EDR filename from which the RDR was
generated.
START TIME - SCLK time of first record in data set.
END TIME - SCLK time of last record in data set.
X_RECORDS - Number of data points in time-series.
In each case these parameters are followed by the equation or
equations used to convert the raw DN values from the EDRs to the
calibrated RDR physical unit values. In the PT case, the header
table is followed by a conversion factor table that contains the
conversion factors used in the DN to physical units equations. The
conversion values found in the RDRs are the definitive values.
The CV and CV data types contain the following header information:
WCL_CELL - Number of the WCL cell (0-3)
CMD_Time - This is the time that the command was issued
from the spacecraft computer to the MECA
subsystem across the serial interface. Units
are seconds of Spacecraft Clock (SCLK).
Read_time - This is the time that the data was returned
to the spacecraft computer across the serial
interface from the MECA subsystem. Units are
seconds of Spacecraft Clock (SCLK)
Mode - The instrument mode
CV = 1
DO = 2
ASV = 3
CP_S1 = 4
CP_S2 = 5
CP_P = 6
Gain - The instrument gain setting which can equal 1,2,3,
4,5,6,or 7.
mVMin or nAMin - The minimum scan value
mVMax or nAMax - The maximum scan value
CV_Scan_rate or CP_Scan_time - Time of scan or rate of
scan in seconds.
Number_of_Samples - Number of samples in the scan,
maximum value is 2015.
The CV and CP header information is preceded by the DN to
physical unit conversion factors. The RDRs are the definitive
source for the conversion factors. The WCL calibration report,
located in the Calibration directory of this archive, is the
definitive source for the conversion equations.
WCL Processing
==============
WCL RDR data products will be generated by the MECA Science Team
using software at the SOC, JPL or their home institutions. The
RDRs produced will be 'processed' data (NASA Level 1). The input
will be one or more MECA non-imaging EDR or RDR data products and
the output will be formatted according to the MECA Non-Imaging RDR
SIS. In general, the processing involved in creating the MECA
Non-Imaging RDRs is a conversion from EDR DN values to physical
units using conversion equations and factors derived from ground
based instrument calibrations. The details of the conversion
equations and factors can be found in the MECA Non-imaging RDR
SIS and the WCL Calibration report, both found in this archive.
WCL Data
========
ISE
---
The ISE data type contains the mV value for each ISE sensor
reading in the RDR. The readings are a result of a potential
across the sensor's membrane/solution interface, the value of
which is dependent on the activity of the selected ionic species
in the beaker solution.
CND
---
The MECA electrical conductivity (EC) data type holds the EC
measurements in a time-series of two ranges of microsiemen per
centimeter. The EC of a solution is a measure of its ability to
carry a current and is thus directly proportional to the total
concentration of dissolved ionic species in the water.
CV
--
The CV data type contains a time-series of electrode potential
(mV) and current (nA) data for measurements made by Conventional
cyclic voltammetry using either a macro-electrode or an array of
micro-electrodes; Anodic Stripping Voltammetry using the
micro-electrode; and a Dissolved Oxygen measurement acquired
with an ion selective electrode with CV-style detection.
CP
--
The CP data type contains a time series of electrode potential
(mV) and current (nA) data for measurements made with one of
the three CP electrodes mounted in the WCL beaker walls. The CP
electrodes include: two 1 mm diameter Ag electrodes (CP_S1 and
CP_S2) and one 1 mm diameter Pt (CP_P) electrode. In a WCL CP
measurement, which is sometime referred to a coulombic
titration, the electrochemical cell potential is measured as
the current is stepped (or ramped) from zero to a set current.
PT
--
The PT data type contains time-series data of pressure
measurements of the internal pressure sensor as well as
temperature data from each of three sensors mounted on the
water tank, the sample drawer, and in the beaker wall. The
pressure and temperature readings apply to the active WCL cell
(known from the command history), and the units of the RDR data
are mbar for pressure and Celsius for temperature. The tank
sensor is used to monitor and verify thawing of the stored
leaching solution, while the drawer sensor monitors the
operation of sample introduction and reagent addition actuators.
The beaker sensor is critical for analysis of chemical data.
WCL Ancillary Data
==================
Ancillary data needed to convert any of the WCL data types from
raw EDR DN values to physical units are given in the individual
RDRs. Additional information on sensor calibrations can be found
either in the WCL calibration report (Calibration Directory of this
archive) or in [KOUNAVESETAL2008].
The ISE, CND and PT data types also contain an events table that
records various events over the course of the sample analysis.
This table records such things as the time of sample delivery to
the analysis cell, and the time of additions to the sample. A
full description of the events can be found in the MECA
Non-Imaging RDR SIS.
WCL Coordinate System
=====================
Information pertaining to where each of the four samples (one per
WCL cell) were taken is recorded in the sample OPS_TOKEN, found
in the file name of each RDR. The OPS_TOKEN can be used to relate
the RDRs to information from the Robotic Arm (RA). The RA is used
to scoop Martian soil into the MECA WCL. Correlation of the RA
OPS_TOKENs to the MECA WCL RDRs will give the users information
about the conditions under which each sample was collected.
WCL Software
============
No WCL specific software will be provided at this time. As the
data products are ASCII, any software that can handle ASCII files
can be used to view the products.
WCL Media/Format
================
As part of the MECA Non-Imaging RDR data set, WCL RDRs will be
delivered using Internet file transfer
protocol. Data formats will be based on standards for such
products established by the Planetary Data System (PDS)
[PDSSR2001].
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