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MSL data in the PDS and the Analyst's Notebook, Working with the archived science & engineering data
jmknapp
post Mar 20 2013, 07:13 PM
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They released some more sol 0-89 data to the PDS today:

The NASA Planetary Data System announces Part 2 of the first release of data from the Mars Science Laboratory (MSL) mission, covering data acquired on Sol 0 through Sol 89, August 6 through November 5, 2012. Part 2 consists of derived data products. Release 1, Part 1, took place on February 27, 2013, and consisted of raw data products.

Part 2 consists of derived data sets from the following instruments:
Alpha Particle X-ray Spectrometer (APXS)
Chemistry and Mineralogy (CheMin)
Hazard Avoidance Cameras (Hazcam)
Navigation Cameras (Navcam)
Rover Environmental Monitoring Station (REMS)
Sample Analysis at Mars (SAM)

Release of the following data sets has been delayed. The data sets will be released as soon as they are made available to PDS.

Chemistry & Micro-Imaging (ChemCam) derived data
Chemistry and Mineralogy (CheMin) raw data
Dynamic Albedo of Neutrons (DAN) derived data
Radiation Assessment Detector (RAD) raw and derived data

Release 1 does not include data from the MAHLI, MARDI, or Mastcam instruments.

Links to all MSL data sets may be found on the PDS Geosciences Node web site http://pds-geosciences.wustl.edu/missions/msl/. The data may also be reached from the main PDS home page, http://pds.nasa.gov/. MSL data are archived at the PDS Atmospheres, Planetary Plasma Interactions (PPI), Geosciences, Imaging, and Navigation and Ancillary Information Facility (NAIF) Nodes.

PDS offers two services for searching the MSL archives:
The Planetary Image Atlas at the Imaging Node allows selection of MSL image data by specific search criteria.
http://pds-imaging.jpl.nasa.gov/search.

The MSL Analyst's Notebook at the Geosciences Node allows searching and downloading of all MSL data in the context of mission events.
http://an.rsl.wustl.edu/msl.

Some documents in the MSL archives are awaiting clearance by JPL Document Review and/or the JPL Import/Export Control Office. They will be posted online as soon as clearance has been received, and announced on the web site http://pds-geosciences.wustl.edu/missions/msl.

To receive email announcements of future releases of MSL data, please sign up on the PDS Subscription Service at http://pds.jpl.nasa.gov/tools/subscription_service/top.cfm.

The PDS Team

Mailto: pds_operator@jpl.nasa.gov


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PaulH51
post Mar 21 2013, 12:10 PM
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QUOTE (jmknapp @ Mar 21 2013, 03:13 AM) *
They released some more sol 0-89 data to the PDS today:

Thanks Joe,

I am going through the PDS learning curve, and learning a little, but still have a lot to learn. Can I ask if you have found any "REMS Ground Temperature" info in the PDS? I saw your posts in another thread regarding 'REMS Air Temperature' Thought it best to post here this time.


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Gerald
post Mar 21 2013, 12:22 PM
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The ground temperature may most likely be provided by some of the thermopiles. With thermopiles you can measure temperature from a distance.
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jmknapp
post Mar 21 2013, 07:16 PM
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Haven't looked at it closely myself yet, but I think the column definitions are in this file:

http://atmos.nmsu.edu/PDS/data/mslrem_1001/LABEL/ENVRDR1.FMT

...and as Gerald says, look for the thermopile data, such as:

QUOTE
COLUMN_NUMBER = 17
NAME = "BRIGHTNESS_TEMP_A"
UNIT = "KELVIN"
FORMAT = "F7.2"
DESCRIPTION = "Brightness temperature of the GTS Thermopile A
(band 8-14 um)"
DATA_TYPE = ASCII_REAL
START_BYTE = 187
BYTES = 7


So that looks like it might even be calibrated to temperature (K), although it's brightness temperature which I gather is not the same as "real" ground temperature ("kinetic temperature") from this reference:

Description of the REMS Ground Temperature Sensor aboard MSL NASA mission to Mars



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PaulH51
post Mar 21 2013, 09:43 PM
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QUOTE (jmknapp @ Mar 22 2013, 03:16 AM) *
...and as Gerald says, look for the thermopile data, such as:

Many thanks Gerald and Joe smile.gif


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jmknapp
post Mar 25 2013, 04:47 PM
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OK, here's a taste of some calibrated REMS data, the brightness temperature of ground temperature sensor A during sol 89:

Attached Image


The sensor looks at the infrared in the band 8-14 um. Looks pretty noisy, particularly at night. Note that brightness temperature is different than actual temperature. There must be some conversion formula?

The data file for that is:

RME_405347393RNV00890000000_______P1.TAB


Generally the files with the temperature readings have "RNV" in the file name.

The column definitions are here:

ENVRDR1.FMT


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mcaplinger
post Mar 25 2013, 05:04 PM
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QUOTE (jmknapp @ Mar 25 2013, 09:47 AM) *
Note that brightness temperature is different than actual temperature. There must be some conversion formula?

You need to know, or assume, the emissivity of the surface in order to do that conversion. The brightness temperature is the temperature that a black body of the observed IR radiance would have.


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Disclaimer: This post is based on public information only. Any opinions are my own.
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jmknapp
post Mar 25 2013, 05:40 PM
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That would explain how it's a bit high.

According to the reference above:

QUOTE
The use of two different bands to measure ground temperature allows the estimation of the emissivity of the surface by means of colour pyrometry algorithms.


...so the ground temperature reading is evidently a function of the thermopile A & B readings.


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Gerald
post Mar 26 2013, 11:52 AM
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You'll be close to a solution by dividing the two values, because (by gray-assumption) the emissivity cancels out, see http://en.wikipedia.org/wiki/Pyrometer.

Then by applying Planck's, or for simplicity, Wien's law you may get close to the absolute temperature, see http://en.wikipedia.org/wiki/Wien_approximation.

My rough approximative ad-hoc idea is, to divide the values of Wien's (or better Planck's) law for the respective mean measured wavelengths for any given fixed temperature, and compare it with the measured quotient.
More accurately, Planck's curve for a fixed temperature multiplied by the sensivity of the respective thermopile (as a function of wavelength) has to be integrated over the wavelength.

The underlying principle is, that the quotient of the emissions of a black or grey body at two fixed wavelengths is temperature-dependent, and provided by Planck's law. Restricted to an appropriate temperature interval the quotient determines temperature uniquely.

Some adjustment might be necessary due to IR absorption by CO2 or dust coating. This may be a second step.

EDIT: By the two values I meant the sensor values as defined in raw data, B1_IR_OUT_2 and B1_IR_OUT_3, rover-induced fluctuations removed, and calibrated for power or radiance. It's not easy, nevertheless.
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jmknapp
post Mar 27 2013, 01:37 PM
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I had a feeling calculus might be involved--a more direct route would be to get the paper submitted to the EGU by Gomez-Elvira et al, maybe they said exactly what they do.

Failing that, wouldn't the brightness temperatures in effect already be the result of integration or other analysis of the raw data? I.e., a sample at a particular time says that the ground looks like a gray body radiating at 265K for the A band (8-14 um) and 273K for the B band (16-20 um). Maybe the conversion to actual temperature from those data points isn't too involved.

P.S. I'm trying to track down this reference cited by the authors:

http://www.ncbi.nlm.nih.gov/pubmed/16642125


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mwolff
post Mar 27 2013, 02:11 PM
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If you are after ground temperature, then the Zorzano reference will not really help. They are using measurements at two different temperatures (and two channels) to reduce the uncertainty associated with the instrument calibration. They are interested in the time series of temperature differences because this is the more important quantity in sensible heat flux characterization. As mentioned by M. Caplinger above, you need to know the emissivity of the material to get absolute temperature. The observed radiance is equal to the emissivity times the Planck function (ignoring atmospheric effects); calculus not needed if you believe your assessments of radiance and emissivity. The hard part, and the subject of the Zorzano paper, is dealing with getting radiance accurately from the instrument measurements. If you want to send me a message, I am sure that one can find you a copy of that paper.
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jmknapp
post Mar 27 2013, 04:11 PM
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The thing is, the emissivity can't be determined a priori, right?

Thanks for the offer, but I was able to get a copy of the paper. By taking the measurements at two different temperatures (in practice, two different times of day) and two wavelength bands it looks like they were able to get within maybe 6K on the individual measurements and less than 1K for the difference.


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Gerald
post Mar 27 2013, 05:02 PM
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The paper can be read online here.
Now I understand better how the thermopiles work internally.
But I didn't find an answer, how to estimate the emissivity; there is mentioned an estimate of somewhere between 0.9 and 1.0, depending on the composition of the ground.
A 10% uncertainty means up to about 27K near 0°C.
The influence of reflected sun light is estimated to be below 0.5%.

As quotient of the Planck function for Kelvin temperature T, and two different wavelengths frequencies nu and mu, I got
(nu/mu)^3 x exp(4.8 x 10^-11 x [(mu-nu)/T] s K),
s = second, K = Kelvin, 4.8 x 10^-11 is Planck's constant h divided by Boltzmann's constant k.
(no errors assumed)
This avoids emissivity by cancelling out, if it is assumed to be the same for both wavelength frequency bands.

By taking 11 um for mean wavelength thermopile A and 18 um for mean wavelength thermopile B, one could try to avoid calculus in a first attempt.

Using the brightness temperatures instead of the radiance sounds good, especially because they will already be calibrated. I'll need to think a bit, how to do it exactly.

EDIT: The above formula just shows, how emissivity cancels out, but to be useful, integrals of the Planck function over the respective wavelengths have to be divided, with the same cancellation effect. Hard to avoid calculus or a numerical solution at the end.

With the very rough assumptions and the formula above, and without calculus, I get
T = 509 K / ln (0.228 q), with q = I(18 um) / I(11 um).
Still to solve is, how to calculate I(18 um) and I(11 um) from the brightness temperatures.

P.S.: In the meanwhile I found the calculus version here. (The paper uses the wavelength version of Planck's law.)
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mwolff
post Mar 28 2013, 03:14 PM
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QUOTE (jmknapp @ Mar 27 2013, 10:11 AM) *
The thing is, the emissivity can't be determined a priori, right?


Not in the way you are suggesting. With wavelength resolution and broad enough coverage, IR remote sensing has "exploited" the Christiansen frequency to have a region where the emissivity was ~1. You are probably aware of the TES products, but just in case:
(http://tes.asu.edu/products/). This approach is much more applicable from orbit, unfortunately.
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jmknapp
post Mar 28 2013, 11:59 PM
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Just going by some comments in the Zorzano paper.

QUOTE
Let us perform two measurements... with two sensors operating at different wavelengths... Standard two-color pyrometric techniques use the ratio...

All the geometrical dependencies cancel out, but any wavelength-dependent factor remains. (For instance, the medium absorption, sensor response, and target emissivity may differ from one wavelength to the other.)


Also, they say regarding the Planck equation:

QUOTE
This is true for a perfect blackbody radiator, but in the general case the radiance must be multiplied by the emissivity. The emissivity is a wavelength-dependent quantity that depends mostly on the material’s exact composition as well as the surface roughness, angle of observation, surface oxidation and contamination, particle size, level of compaction, etc. These factors are difficult to be known accurately a priori...

The user must know the emissivity to get the correct temperature value; thus this technique is not useful to explore unknown targets. In ratio pyrometry intensities are measured simultaneously at two different wavelengths and divided. The resulting representative equation is solved for temperature assuming that the spectral emissivities in both ranges are equal and are canceled in the division. This method works only if the emissivity is the same at both wavelengths, but, again, it is not useful for a general case.


They don't talk about Christiansen frquency but that sounds interesting. Thanks for the link to the TES maps.


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