SMALL LIDAR FOR PROFILING WATER VAPOR, AEROSOLS AND
WINDS FROM A MARS LANDER
J. B. Abshire1,2, D. R. Cremons2, K. Numata2, S. D. Guzewich2,
M. D. Smith2, X. Sun2
1

University of Maryland, Astronomy Department, College Park MD 20740 USA (james.b.abshire@nasa.gov)
2
NASA Goddard Space Flight Center, Greenbelt MD 20771 USA

Introduction:
The planetary boundary layer (PBL) is the
lowest layer of the atmosphere that interacts directly
with the surface. Processes within the Mars PBL are
very important scientifically because they control the
transfer of heat, momentum, dust, water, and other
constituents between surface and atmospheric reservoirs [1]. Understanding these processes is critical
for understanding the modern climate, including the
stability and development of the polar caps [2], how
the regolith exchanges with the atmosphere [3], how
wind shapes the landscape [4], how dust is lifted and
transported [5], and for being able to validate and
improve general circulation models (GCMs). The
PBL is also important for operations since it is the
environment in which landed missions must operate.
On Mars the PBL depth varies between roughly 1
and 10 km, depending on time of day, with the deepest layer occurring during the day when convective
turbulence is greatest.
The PBL is difficult to observe from orbit, and
so detailed observations of it have been mostly limited to those just at the surface from landers. The
lack of PBL observations has led to significant gaps
of understanding in several key areas. These include
diurnal variations of aerosols and water vapor, and
direct measurements of wind velocity, the combination of which provides information on the horizontal
and vertical transport of water, dust, and other trace
species and their exchange with the surface. Because
these quantities are interrelated [6,7] and they partially drive the wind fields, it is important to measure
the water vapor, aerosols, and winds simultaneously,
ideally using a single instrument.
Measurement Approach:
We are developing and plan to demonstrate a
breadboard of a small atmospheric lidar to address
these needs for a future lander on Mars [8]. As
shown in Figures 1 and 2, our new lidar approach is
to remotely profile aerosols, atmospheric water vapor and winds using laser wavelengths near 1911
nm. The lidar is designed to measure vertically resolved profiles of water vapor by using a single frequency laser. The laser will be tuned onto and off
strong isolated water vapor lines near 1911 nm as
shown in Figure 3. The vertical distribution of water
vapor will be determined from the on- and off-line

backscatter profiles via the differential absorption
lidar (DIAL) technique shown in Figure 4. The same
laser is used for measuring the aerosol and wind profiles by tuning the laser off-line and resolving the
Doppler shift in the backscatter profiles. The laser
beam is linearly polarized and a polarization resolved receiver allows separating the backscatter of
water ice from dust. As shown in Figure 1, the lidar
emits two beams that are offset 30 deg from zenith
and perpendicular to one another in azimuth, allowing vector wind profiles to be resolved. Both lidar
view directions are otherwise identical and use
common lens-type receiver telescopes.
These lidar measurements address important science needs that are traceable to Mars Exploration Program Analysis Group (MEPAG) science goals relating to climate, surface-atmosphere
interactions, and preparing for human exploration.
Our lidar will measure vertical profiles of water vapor, and dust and water ice aerosols and winds with
km-scale vertical resolution from 100 m above the
surface to > 15 km altitude. These measurements
will directly profile the full planetary boundary layer, which is key for understanding how water, dust,
CO2 and trace species exchange between surface and
atmosphere. The lidar will provide observations of
these profiles simultaneously during a nominal 4minute averaging time. A summary of the lidar’s
calculated measurement performance is shown in
Table 1.
Technology and Development Plan:
Our lidar approach shown in Figure 5 utilizes a new laser diode seeded Thulium fiber-based
laser transmitter and a highly sensitive HgCdTe avalanche photodiode detector in the receiver. We have
procured all components to demonstrate a breadboard version of a single lidar channel. During the
next 12 months our plan is to complete testing and
assembly of the lidar components to a system TRL 4.
We then plan to use the breadboard lidar to demonstrate profile measurements of aerosols, water vapor
and wind from the Mauna Kea Hawaii astronomy
site where relatively dry atmospheric conditions reduce absorption of the 1911 nm laser signal.
Acknowledgement: This work is supported by an
award from the 2019 NASA PICASSO program.

References:
[1] Read, P.L., Lewis, S.R., Mulholland, D.P., 2015. The physics of Martian weather and climate: a review. Reports Prog. Phys. 78, 125901. https://doi.org/10.1088/0034-4885/78/12/125901
[2] Piqueux S., Kleinböhl A., Hayne P. O., Kass D. M., Schofield J. T. and McCleese D. J., 2015 Variability of
the martian seasonal CO2 cap extent over eight Mars years. Icarus 251, 164–180
[3] Daerden F., Whiteway J. A., Davy R., Verhoeven C., Komguem L., Dickinson C., Taylor P. A. and Larsen
N., 2010 Simulating observed boundary layer clouds on Mars. Geophys. Res. Lett. 37, L04203
[4] Greeley, R., Thompson, S.D., 2003. Mars: Aeolian features and wind predictions at the Terra Meridiani and
Isidis Planitia potential Mars Exploration Rover landing sites. J. Geophys. Res. 108.
https://doi.org/10.1029/2003JE002110
[5] Spiga A. and Lewis S. R., 2010 Martian mesoscale and microscale wind variability of relevance for dust
lifting. Int. J. Mars Sci. Explor. 5, 146–158
[6] Smith, M.D., 2004. Interannual variability in TES atmospheric observations of Mars during 1999–2003. Icarus 167, 148–165.
[7] Smith, M.D., 2008. Spacecraft Observations of the Martian Atmosphere. Annu. Rev. Earth Planet. Sci. 36,
191–219. https://doi.org/10.1146/annurev.earth.36.031207.124334
[8] J. Abshire, S. Guzewich, D. Cremons, M. Smith, K. Numata, and X. Sun, Small Lidar for Profiling Water
Vapor, Aerosols and Winds from Planetary Landers, Europlanet Science Congress 2021, EPSC2021-136,
https://doi.org/10.5194/epsc2021-136.

Figure 1. (Left) Concept sketch of the two laser beams exiting the small lidar on a lander. The blue color denotes the 1911 nm beams used for the water vapor profiles and vector wind profiles. (Right) Solid view of the
lidar instrument concept. The approximate dimensions of the box at the bottom are 30 x 18 x 8 cm, and the larger cones are the lidar receiver’s lens assemblies. The lidar will measure for the first time vertically resolved water vapor and wind profiles, and aerosol profiles, in the Mars PBL.

Figure 2. Illustration of the lidar’s vertically resolved measurements, made from the surface to ~20 km every
~20 minutes. The lidar will provide, for the first time, vertically-resolved water vapor and wind profiles, along
with aerosol profiles, in the Mars boundary layer.

Figure 3. Plots of Mars atmospheric transmission km in 1911 nm region calculated from the surface to 20 km.
The dotted boxes correspond to the spectral regions shown in the lower frames. The water vapor absorption
lines near 1911 nm are well-suited for DIAL lidar for Mars, and the selected water vapor line is chosen based on
abundance, which ranges from 5 to 50 pr-µm. The rightmost plot shows that the 1910.5 nm region may be used
for a DIAL lidar demonstration at Mauna Kea to ~ 1-km altitude.

Figure 4. Concept for the DIAL lidar measurement of water vapor profiles showing the stronger backscatter
profile for the off-line (blue) wavelength, and weaker profile (due to water vapor absorption) of the on-line
wavelength.

Figure 5. Simplified block diagram of the lidar. The small lidar uses a single-frequency tunable 1911 nm laser
and a sensitive 4-pixel detector to measure water vapor, wind and aerosol profiles.

Table 1 - Summary of calculated lidar measurement performance.
These are based on a detailed lidar backscatter measurement model, and are for 250 sec averaging time, 1-km
bins, 0.5-W average laser power.

Parameter
1 km
5 km
10 km
Water Vapor rel. error* in alt bin (%)
<0.2
1
15
Aerosol profile Relative error (%)
<0.02
0.01
0.04
Horizontal Wind speed error (m/sec)
<0.02
0.1
0.6
* based on 15 pr-um WV total with uniform mixing ratio from 0-15 km

15 km
110
1
2

20 km
-3
5