Using Emirates Mars Infrared Spectrometer (EMIRS) Science Observations to
Analyze Diurnal Temperatures and Characterize Thermophysical Properties
N. AlMheiri, Mohammed Bin Rashid Space Centre, Dubai, UAE (Noora.almehairi@mbrsc.ae), M. Yousuf,
Mohammed Bin Rashid Space Centre, Dubai, UAE, C. S. Edwards, Northern Arizona University, Department
of Physics and Astronomy, Flagstaff, AZ, USA, M. Osterloo, Space Science Institute, Boulder, CO, USA, M.
Wolff, Space Science Institute, Boulder, CO, USA.
Introduction:
The Emirates Mars Mission (EMM), launched on
July 20, 2020, is the United Arab Emirates’ (UAE)
first mission to Mars and the Arab World’s first
mission to another planet. EMM is designed to study
the dynamics of the Martian atmosphere on a global,
diurnal, and seasonal timescales using three
instruments onboard a spacecraft named the Hope
Probe. Two of EMM’s instruments, the Emirates
eXploration Imager (EXI) [Jones et al. 2021] and
Emirates Mars InfraRed Spectrometer (EMIRS)
[Edwards et al. 2021], focus on the lower
atmosphere. The third instrument, Emirates Mars
Ultraviolet Spectrometer (EMUS) [Holsclaw et al.
2021], focuses on studying the Martian thermosphere
and exosphere. The combination of instruments and
the temporal and spatial sampling of the mission will
be suited to perform studies to better understand the
relationship between the atmosphere and surface.
The science phase of the mission commenced on
May 23rd, 2021, and the data of the three
instruments became publicly available on October
1st, 2021[Amiri et al. 2022]. The Martian surface is
known to display a high degree of variability in
thermophysical properties between different regions
as different types of surfaces and mixed materials
respond differently to heating and cooling depending
on their thermal inertia [Jakosky et al. 2000].
Thermal inertia is a thermophysical property of a
material that represents the measure of material
responses to changes in temperature. In addition,
oscillations in the Martian surface temperature are
primarily determined by its thermal inertia. The
thermal inertia of the Martian surface depends on its
particle size and degree of compaction/cementation
within the topmost part of the surface, and it is
independent of local time, latitude, and season
[Fergason et al. 2006]. The work presented here
using EMIRS data is a continuation of previous work
[Yousuf et al. 2021] done using Mars Global
Surveyor’s (MGS) instrument Thermal Emission
Spectrometer (TES) Aerobraking data which
provided nearly complete diurnal coverages near the
poles. For EMIRS data, currently, the majority of the
diurnal coverage within a 5 by 5 degrees grid is
found closer to the equator.

Research Objective:
Here we present a preliminary study on the
best-fit estimates of thermal inertia derived using the
KRC Thermal Model [Kieffer 2013] for observed
diurnal temperatures taken by EMIRS instrument
during the Science Phase. The ultimate goal will
eventually be to compare the results of this study
with previously undertaken work using TES
Aerobraking data [Yousuf et al. 2021].
Data and Tools:
EMIRS is an interferometric thermal infrared
spectrometer that characterizes the lower atmosphere
of Mars by taking measurements of infrared radiance
and determining the distribution of lower
atmospheric constituents such as dust, water ice, and
water vapor optical depths, in addition to Mars
surface and atmospheric temperature profiles up to
50 km from the surface with a vertical resolution of
~10 km. EMIRS operates in the 6-40+ μm range
with 5 cm-1 and 10 cm-1 spectral sampling
[Edwards et al. 2021]. JMARS software is used to
query the hosted EMIRS science observation,
investigate the general geologic characteristics of the
selected regions of interest, as well as access the
KRC numerical thermal model for thermal inertia
analysis. KRC has the ability to compute the
temperature of the surface as a function of
time-of-day, latitude, season, and a multitude of
physical parameters [Kieffer, 2013]. JMARS is a
java-based package developed by Arizona State
University that provides a layered system, whereby
data from different sources and missions can be
extracted, colorized, scaled, blended, merged, and
superimposed on one another [​​Dickenshied et al.
2014].
Methodology:
The methodology followed in this study is
analogous to our previous work [Yousuf et al. 2021].
Using EMIRS data, several geographic locations
displaying reasonable diurnal coverage and
homogeneous surface properties within a 5 by 5
degree grid were chosen on Mars. This is important
as there is important thermophysical information that
is discernible using the full diurnal curve (e.g.,

different types of surfaces and mixed materials
respond differently to heating and cooling depending
on their thermal inertia). Using THEMIS nighttime
and daytime infrared data, morphological and
thermophysical properties of the selected ROIs were
closely examined. Next, the average brightness
temperatures of the selected ROIs were computed
using two portions of the spectrum;
● short wavenumbers (i.e., 1290 - 1311 cm-1),
near this wavenumber, the atmosphere of
Mars is almost transparent, i.e., the radiance
is not absorbed by atmospheric gasses and
aerosols. Thus, the surface temperature is
represented by obtaining the brightness
temperature at that wavenumber following
the methods from [Edwards et al. 2021];
and
● long wavenumbers (i.e., 306.83 – 497.27
cm-1) following the work of [Kieffer et al.
2000], and [Kieffer et al. 2001], for cold
surfaces, near this wavenumber region gives
the most consistent surface kinetic
temperature estimate as it is least affected
by dust and CO2 properties.
Using KRC Thermal Model (JMARS) [Christensen
et al. 2009] and [Kieffer 2013], best-fitting thermal
inertia with EMIRS observed temperatures at all
times of the day were derived, where thermal inertia
was set in the range 50 - 600 J·m-2·K-1·s-½ at
equally spaced steps of 50 J·m-2·K-1·s-½. Other
parameters, such as Geographic Coordinates, Solar
Longitude, and Albedo were the average of the
points corresponding in each ROI. Based on the fit
noticed between EMIRS observed (both calculated
over short and long wavenumber) to the modeled
temperatures, a hybrid version of the EMIRS
temperatures having a combination of temperatures
from short and long wavenumbers at a specific time
cut-off was constructed taking into consideration the
following: for hours before 6 am and after 6 pm were
seen to be best fitted by long wavenumber, while
hours between 6 am and 6 pm were best fitted by
short wavenumber. To determine which thermal
inertia output of the KRC Model best fits all the
temperatures observed by EMIRS (the non-hybrid
and hybrid versions) at all different local times,
comparison plots were produced, statistical analyses
of the Chi-squared test were performed using the
modeled and observed data, and the results were
compared to the measurements reported previously
by the other missions.

Preliminary Results:
By comparing the Hybrid version of EMIRS
observed temperatures modeled using the KRC
Thermal Model to find the best estimates of thermal
inertia, it has been noticed that in some ROIs, we see
a fit happening at all local times with a value of
thermal inertia that is analogous to some degree to
what has been reported by previous instruments.
While other ROIs do not entirely have all local times
fitted, this is often accompanied by a different value
of thermal inertia, contrary to what has been reported
previously by other studies using different
instruments (Figure 1, and Table 1).
The inconsistent results seen in Figure 1 might be
due to the following:
1. assuming the ROI is homogeneous and that
all the points within the same ROI have the
same geology, when in reality, the points
may not be of the same geologic material.
2. errors in equating different atmospheric
factors while deriving the temperatures
using the KRC Thermal Model. Which may
suggest the utility of a hybrid model with
temperature cut-off instead.
Diurnal coverage allows one to investigate the
heterogeneity of a geographic surface, indicating that
some temperatures may come from different surface
types within the ROI, as seen in Figure 1. This
suggests that we need to consider the implications of
different surfaces within an EMIRS pixel (i.e., it has
the smallest instantaneous field of view 5.5 mrad,
enabling small footprints from large distances
[Edwards et al. 2021]).

Figure 1. The line graphs on Top compare
model-simulated temperatures using the KRC
Thermal Model (multi-colored lines, each line
depicting temperature variation of a specific value of
thermal inertia incremented from 50 to 600
J·m-2·K-1·s-1⁄2 at equally spaced steps of 50
J·m-2·K-1·s-1⁄2) against EMIRS temperature
observations calculated over short (magenta line) and
long (black line) wavenumber separately, at different
times of the day (x-axis) at a selected study region.
Plot on the Bottom show model-simulated
temperatures (multi-colored lines) plotted against the
result of the hybrid version of the EMIRS
temperature observations (black dashed line)
constructed using a combination of short (magenta
circles) and long (black circles) wavenumber
temperatures based on time of the day cut-offs.

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Table 1 shows chi-squared results for a best-fit
estimate of thermal inertia for all the three different
scenarios (i.e., short wavenumber, long wavenumber,
and the hybrid version), along with measurements
reported by other studies using different instruments.
The suggested thermal inertia from two out of three
scenarios was found to be the same across ROI-1 at
100 tiu (Figure 1), and comparing this to what
previously has been reported in TES and THEMIS
thermal inertia maps available in JMARS, TES
daytime measurement is considered the closest with
thermal inertia of 147 tiu. Surface materials
exhibiting low values of thermal inertia are classified
under ‘fine grained and loosely packed’.
Future Work:
We will present the initial results and discuss the
findings of various ROIs in our study for finding the
best fit estimates using EMIRS diurnal observations
and showcase the utility of a hybrid model. We
currently use a time-of-day cut-off to construct the
hybrid version of EMIRS temperature observations
and we plan to change it to a temperature cut-off
instead.

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