1. Tropical
Cyclone
Observa2ons
with
Aircra7
Passive
and
Ac2ve
Microwave
Instruments
Paul
Chang
and
Zorana
Jelenak,
NOAA/NESDIS/STAR
James
Carswell,
Remote
Sensing
Solu2ons
Stephen
Frasier,
University
of
MassachuseLs
1
IGARSS
2011
-­‐
26
July
2011
!

2. Mo2va2on
Stepped
Frequency
Microwave
Radiometer
(SFMR)
• Deployed
on
NOAA
research
and
53rd
Air
Force
Reserve
Weather
reconnaissance
aircra7.
• Provides
cri2cal
wind
speed
observa2ons
of
tropical
cyclone
environment
to
forecasters
for
wind
radii
es2ma2on.
• Provides
“surface
truth”
for
geophysical
model
func2on
development
and
valida2on.
Problem:
• SFMR
under
es2mates
precipita2on
rate
within
TCs
…
• Retrieved
wind
speed
and
rain
rate
errors
correlated
…
• Thus
wind
speed
error
depends
on
environment
in
field
of
view
(i.e.
precipita2on).
IGARSS
2011
-­‐
26
July
2011
2
!

3. Measurement
Geometry
IWRAP:
• SFMR
Specifica2ons
Simultaneous,
Mul2-­‐Beam
• Nadir Viewing.
Frequency:
C-­‐band
&
Ku-­‐band
Doppler/Reflec2vity
• C-band – 6 channels.
Polariza2on:
VV,
HH
Profiling
• ~4.7 to 7.2 GHz.
Beam
Incidence
Angles:
30,
35,
41.5,
50
SFMR column
(20-28 deg)ange:
• 00
–
8000
m
Al2tude
R 5 IWRAP
Range
Resolu2on:
• 5,
30,
60
&
120
m
1 C/Ku-band Doppler Radar.
• Conical scanning.
• Four beams.
• 20 to 55 degrees incidence.
Conical
Scan
• 30-m range gates.
(60
rpm)
• NOAA Tail Doppler Radar
• X-band.
SFMR foot print • Helix scan fore/aft 20 deg.
Propor2onally
not
to
scale.
• 75-m range gates.
• Not to scale • NOAA Lower Fuselage Radar
• NOAA Tail Doppler Radar & Lower Fuselage Radar • C-band (~5.3 GHz)
beams not shown
• Reflectivity.
• Near grazing conical scanning.
IGARSS
2011
-­‐
26
July
2011
3
!

4. SFMR
Tb
Geophysical
Model
Func2on
(GMF)
Tb Versus U10N & Frequency Tb Versus Rain Rate & Frequency
3
km
al2tude,
28oC
SST
3
km
al2tude,
28oC
SST
IGARSS
2011
-­‐
26
July
2011
4
!

5. Rain
Rate
Under
Es2mated
IWRAP
derived
aLenua2on
ploLed
versus
SFMR
rain
rate
retrievals.
• Corrected
SFMR
Rain
Rate
=
2.5
x
SFMR
Rain
Rate
–
5
mm/hr.
• Figures
from
[Esteban
Fernandez,
2005];
UMass
SFMR
–
2003
flights.
IGARSS
2011
-­‐
26
July
2011
5
!

6. Rain
Rate
Under
Es2mated
by
SFMR
• SFMR
under
predicts
rain
rate
by
a
factor
of
2.5
• SFMR
rain
rate
es2mates
are
biased
by
~
5
mm/hr.
• Same
results
observed
in
2003
comparison
between
IWRAP
and
UMass
SFMR.
• Comparisons
with
Tail
Doppler
and
Lower
Fuselage
radars
show
same
5
mm/hr
bias
and
SFMR
under
es2mates
rain
rate.
*
NOAA
Aircra7
Opera2ons
Center
SFMR
IGARSS
2011
-­‐
26
July
2011
6
!

7. New
SFMR
Absorp2on
Model
SFMR Absorption Model
Current K =α f ( Rm Rr Fe
)(R )
Re
r
Model
Monte-Carlo: Clustered Solutions
Re Fe Rm Slope (m) Offset (b)
Monte-
0.76 0.0676 2.75 0.947 0.110
Carlo
0.74 0.0696 2.75 0.950 0.138
Solutions
0.74 0.0716 2.8 0.900 0.015
0.72 0.0736 2.8 0.910 -0.109
0.7 0.0756 2.8 0.915 -0.074
* Minimized offset and required slope > .85
IGARSS
2011
-­‐
26
July
2011
7
!

8. New
SFMR
Absorp2on
Model
Old SFMR Model New SFMR Model
SFMR Tb data from Uhlhorn, et al, 2007: Hurricane Surface Wind Measurements from an Operational
Stepped Frequency Microwave Radiometer. Monthly Weather Review, v.135, pp. 3070–3085.
IGARSS
2011
-­‐
26
July
2011
8
!

9. New
SFMR
Absorp2on
Model
–
IWRAP
Comparison
IWRAP Z measurements versus SFMR Rain Rate Retrievals • IWRAP
C-­‐band
reflec2vity
factor
measurements.
• SFMR
rain
rate
derived
using
new
absorp2on
model.
• Solid
black
line
is
opera2onal
Z-­‐R
model
for
tropical
cyclones.
• Red
line
is
fit
to
data
solving
for
exponent
only.
• Green
line
is
fit
to
data
solving
for
exponent
and
mul2plier.
*
2008
IWRAP
and
SFMR
measurements
from
hurricane
season.
IGARSS
2011
-­‐
26
July
2011
9
!

10. Wind
Speed
and
Rain
Rate
Retrieval
Errors
IGARSS
2011
-­‐
26
July
2011
10
!

11. Summary
• SFMR rain rate retrievals have been documented to
under predict the rain rate in tropical cyclones.
• New absorption GMF developed for SFMR for 2005 data
set.
• SFMR wind speed retrievals compared with GPS drop
sondes winds improves with new SFMR absorption
model.
• SFMR rain rate – IWRAP reflectivity factor comparison
improves with new SFMR absorption model.
IGARSS
2011
-­‐
26
July
2011
11
!

12. THANK YOU
Ques2ons?
IGARSS
2011
-­‐
26
July
2011
12
!