Landing Site Surface Characteristics From TES EPF Observations

1
Landing Site Surface Characteristics From TES EPF
Observations

• Joshua L. Bandfield
• Arizona State University

Melas Chasma THEMIS VIS (C. Edwards)
2
Overview

• What are emission phase function (EPF)
  measurements and how do they work?
• How can they be useful for landing site
  characterization?
• Examples of slope retrievals from EPFs
• Example of EPFs and rocky surfaces

Athabasca Valles THEMIS Day IR/MOLA (R. Luk)
3
Emission Phase Function (EPF) Measurements

• EPFs measure a single surface from different
  viewing angles
• Thermal IR spectrometer or bolometer (TES or MCS)
  measurements with spot size of 10s of km
• Similar to visible/NIR phase measurements (e.g.
  HRSC) but not sensitive to solar phase angle

4
Slope Effects in EPF Measurements

• Surface slopes (larger than cm scale) have
  different temperatures based on whether sunlit or
  shaded
• Measured radiance is dependent on viewing angle
  and azimuth

q1
q2
q1
q2
Measured radiance (and apparent surface
temperature) will decrease when passing over the
surface from the left to the right
5
Slope Effects in EPF Measurements
TES EPF Observations
6
4
OCK 10823 (dune field)
2
0
DT (K)
Delta T (K)
-2
-4
-6
-80
-60
-40
-20
0
20
40
60
80
THEMIS VIS
Emission Angle
6
Slope Effects in EPF Measurements
TES EPF Observations
6
4
OCK 10823 (dune field)
2
0
DT (K)
OCK 9938
Delta T (K)
-2
-4
-6
-80
-60
-40
-20
0
20
40
60
80
THEMIS VIS
Emission Angle
7
Slope Effects in EPF Measurements
TES EPF Observations
6
4
OCK 10823 (dune field)
12 Slope Model
2
5 Slope Model
0
DT (K)
OCK 9938
Delta T (K)
-2
-4
-6
-80
-60
-40
-20
0
20
40
60
80
Emission Angle
8
TES EPF Observations
Slope (deg.)

• Phoenix B region landing site EPF data displays
  variations in modeled slopes
• This is currently a critical data product effort

9
TES EPF Observations
Slope (deg.)

• Phoenix B region landing site EPF data displays
  variations in modeled slopes
• This is currently a critical data product effort

Slope (deg.)
10
Slope Effects in EPF Measurements

• Some details
• High solar incidence and viewing aligned with
  solar azimuth increases sensitivity
• Correction for atmospheric and directional
  emissivity effects need to be applied
• Complimentary to slope retrieval techniques using
  MOLA and imaging

11
Effects of Rocks on EPF Observations

• High-inertia rocks make up a larger proportion of
  the field of view at high emission angles

12
Effects of Rocks on EPF Observations

• High-inertia rocks make up a larger proportion of
  the field of view at high emission angles
• This causes a change in apparent temperature with
  changing emission angles

Mini-TES temperatures with Pancam at
Gusev (NASA/JPL/Cornell/ASU)
13
Effects of Rocks on EPF Observations
6

• Rocky surfaces have a symmetrical effect on the
  apparent temperature
• This is most apparent at night or when the solar
  azimuth is orthogonal to viewing azimuth

OCK 8468 EPF 14.5 N, 325.2 E
4
2
0
Delta T (K)
-2
-4
-6
-80
-60
-40
-20
0
20
40
60
80
Emission Angle
14
Technique Development

• Currently allows for qualitative comparisons
  between regions
• More realistic surfaces are necessary to better
  quantify slopes and rocks

J. Byrnes, USGS
15
Summary

• TES EPFs are useful for
• Surface slopes at decimeter and larger scales
• Rock abundances (but how precise/accurate?)
• TES EPFs are currently being targeted for Phoenix
  landing sites
• Will be targeted for MSL sites

Gale Crater THEMIS VIS/Night IR (R. Luk)