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PLMR Calibration
Valerio ParuscioDr Jeff Walker
University of Melbourne
Outline
• Admissible error in brightness temperature measurement
• Available data for calibration
• Calibration options and recommendation
Model Sensitivity Assessment
How accurate has the Brightness Temperature measurement to be in order to have a Moisture content error less than 4%?
Hypothesis:• Roughness = 0.2• SS Albedo = 0.05• Soil Type = Silt clay loam
Variables:• Moisture Content (0.05-0.4) %v/%v• Vegetation Water Content (03)kg/m2
• Soil Temperature (280315)K• Incidence Angle (040)
Model Sensitivity Assessment
How accurate has the Brightness Temperature measurement to be in order to have a Moisture content error less than 4%?
Graphs Tb sensitivity
cold 4.5 3.2 6.8 7.3
hot 5.0 3.6 7.6 8.2
cold 2.2 1.3 3.4 2.9
hot 2.5 1.5 3.8 3.3
0 40 0 40
3 Vegeta
tion
Wate
r Conte
nt
dry wet
0
Moisture Content
Incidence Angle
Soil
Tem
pera
ture
cold 4.5 6.4 6.7 7.0
hot 5.0 7.2 7.6 7.9
cold 2.2 2.6 3.4 2.8
hot 2.5 2.9 3.8 3.2
0 40 0 40
Moisture Content
dry wet
Incidence Angle
Soil
Tem
per
atu
re 0
Veg
etati
on
Wate
r Conte
nt
3
1.3
2.2
H polarization
error (K)
V polarization
error (K)
Critical scenarios• High value of Vegetation Water Content• High Incidence Angle• Dry Soil
Max Tb error permitted =
Most common scenarios• Low value of Vegetation Water Content
Max Tb error permitted =
Commonly Tb error up to 8K can be tolerated
4.7K (Hpol)2.7K (Vpol)
2.2K (Hpol)1.3K (Vpol)
Available data for
calibration• Box pre and post flight
(~300K)
act
ual
measured
Available data for
calibration• Box pre and post flight
(~300K)
• Sky pre and post flight (~5K)
act
ual
measured
Box and Sky Brightness Temperature
Pre flight Box
Pre flight Sky Post flight Sky
Post flight Box
Available data for
calibration• Box pre and post flight
(~300K)
• Sky pre and post flight (~5K)
• Water in flight (~110K)
act
ual
measured
Temperature and Conductivity spatial series
Temperature and Conductivity time series
Transect–Buoy data comparision
Week 1 Week 2 Week 3 Week 4
Thermal Infrared data over the lake
Mon
Tue
Wed
Thu
Fri
Available data for
calibration• Box pre and post flight
(~300K)
• Sky pre and post flight (~5K)
• Water in flight (~110K)
• Sky in flight (~5K)
act
ual
measured
Available data for calibration
1. Box pre flight (~300K)
2. Sky pre flight (~5K)
3. Water in flight (~110K)
4. Sky in flight (~5K)
5. Box post flight (~300K)
6. Sky post flight (~5K)
act
ual
measured
Calibration options• 6 points (all)
• 4 points/2 points (box & sky from the ground)
• 3 points (box and water)
Calibration lines (6 beams, 2 polarizations)
Check the 4 pt calibration with water ponit
H polV pol
Check the 3 pt calibration with in flight sky ponit
V pol H pol
Variation in Tb measurement passing from the 4 points cal to
the 3 points cal
Time series of slope & offset (4 pts)
• From 4 pt
V-Pol
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
30/10/05 4/11/05 9/11/05 14/11/05 19/11/05 24/11/05 29/11/05
Date
Off
se
t (K
)
V3L
V2L
V1L
V1R
V2R
V3R
H-Pol
-40
-35
-30
-25
-20
-15
-10
-5
0
5
30/10/05 4/11/05 9/11/05 14/11/05 19/11/05 24/11/05 29/11/05
Date
Off
se
t (K
)
H3L
H2L
H1L
H1R
H2R
H3R
V-Pol
0.95
0.97
0.99
1.01
1.03
1.05
1.07
1.09
1.11
1.13
1.15
30/10/05 4/11/05 9/11/05 14/11/05 19/11/05 24/11/05 29/11/05
Date
Slo
pe
(K
/K)
V3L
V2L
V1L
V1R
V2R
V3R
H-Pol
0.95
0.97
0.99
1.01
1.03
1.05
1.07
1.09
1.11
1.13
1.15
30/10/05 4/11/05 9/11/05 14/11/05 19/11/05 24/11/05 29/11/05
Date
Slo
pe
(K
/K)
H3L
H2L
H1L
H1R
H2R
H3R
Variation in Tb measurement passing from the 4 points cal to
the 2 points cal
Error using a unique 4 pt calibration instead of a daily one
Conclusion
• Recommendation this campaign
V pol 4 pt dailyH pol 4 pt daily (or unique)
next campaign V pol 4 pt daily, 3 pt(?)
H pol 4 pt/2 pt daily (or unique)