!

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  

IGARSS  2011  -­‐  26  July  2011  1  

!

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  

!

Measurement  Geometry  

IGARSS  2011  -­‐  26  July  2011   3  

                                           Specifica2ons    

Frequency:  C-­‐band  &  Ku-­‐band  Polariza2on:  VV,  HH  Beam  Incidence  Angles:  30,  35,  41.5,  50  Al2tude  Range:  500  –  8000  m  Range  Resolu2on:  15,  30,  60  &  120  m    

Propor2onally  not  to  scale.  

Conical  Scan      (60  rpm)  

IWRAP:      Simultaneous,  Mul2-­‐Beam      Doppler/Reflec2vity      Profiling    

SFMR foot print

SFMR column (20-28 deg)

•  SFMR •  Nadir Viewing. •  C-band – 6 channels. •  ~4.7 to 7.2 GHz.

•  IWRAP •  C/Ku-band Doppler Radar. •  Conical scanning. •  Four beams. •  20 to 55 degrees incidence. •  30-m range gates.

•  NOAA Tail Doppler Radar •  X-band. •  Helix scan fore/aft 20 deg. •  75-m range gates.

•  NOAA Lower Fuselage Radar •  C-band (~5.3 GHz) •  Reflectivity. •  Near grazing conical scanning.

•  Not to scale •  NOAA Tail Doppler Radar & Lower Fuselage Radar beams not shown

!

SFMR  Tb  Geophysical  Model  Func2on  (GMF)  

IGARSS  2011  -­‐  26  July  2011   4  

Tb Versus U10N & Frequency Tb Versus Rain Rate & Frequency

3  km  al2tude,  28oC  SST   3  km  al2tude,  28oC  SST  

!

Rain  Rate  Under  Es2mated  

•  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  

IWRAP  derived  aLenua2on  ploLed  versus  SFMR  rain  rate  retrievals.  

!

Rain  Rate  Under  Es2mated  by  SFMR  

IGARSS  2011  -­‐  26  July  2011   6  

•  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  

!

New  SFMR  Absorp2on  Model  

IGARSS  2011  -­‐  26  July  2011   7  

( )( )eeFrm R

rRR RfK α=

Re Fe Rm Slope (m) Offset (b) 0.76 0.0676 2.75 0.947 0.110 0.74 0.0696 2.75 0.950 0.138 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

SFMR Absorption Model

* Minimized offset and required slope > .85

Monte-Carlo: Clustered Solutions

Current Model

Monte- Carlo

Solutions

!

New  SFMR  Absorp2on  Model  

IGARSS  2011  -­‐  26  July  2011   8  

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.

!

New  SFMR  Absorp2on  Model  –  IWRAP  Comparison  

•  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.  

IGARSS  2011  -­‐  26  July  2011   9  

*  2008  IWRAP  and  SFMR  measurements  from  hurricane  season.  

IWRAP Z measurements versus SFMR Rain Rate Retrievals

!

Wind  Speed  and  Rain  Rate  Retrieval  Errors  

IGARSS  2011  -­‐  26  July  2011   10  

!

Summary  

IGARSS  2011  -­‐  26  July  2011   11  

•  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.

!

Ques2ons?  

IGARSS  2011  -­‐  26  July  2011   12  

THANK YOU