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Precipitation Retrieval Accuracies for Geo-Microwave Sounders

David H. Staelin and Chinnawat Surussavadee

Presented at IGARSS ’06

Denver, ColoradoJuly 31, 2006

OUTLINEGeoMicrowave instrument conceptsPrecipitation retrieval methodInstrument optionsMovies: MM5 vs. GEMMovies: GEM and GeoStar comparisonSummary and conclusions

Staelin andSurussavadeeJuly 2006

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NoddingSubreflector

MIT Lincoln Laboratory 1998 GEM study of 2m dish:Can be integrated on GOES

∆Trms ≅ 0.5K (400 GHz, τ = 0.1s) Weight ~40 kg, 130 watts

8 km200 km

8 km/sec

Geo-Microwave Sensor Concepts

Staelin andSurussavadeeJuly 2006

GeoSTAR’

GEM2 meters

2 m

1.2 mGOES

GEM

GeoSTAR

2 mGEM’

Sketch by Ball Sketch by JPLSketch by MIT Lincoln Laboratory

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Original 183±7 GHz 5-km image260 oK

220

180

Blurred 30-km image

Sharpened pattern G’(θ)

30 km

Original antenna pattern

Sharpened 30-km image

~22.5 km

Image Sharpening

Requires Nyquist samplingG’(θ) = Fourier transform {W(fθ)}

To minimize MSE:

Noise increase is acceptable

12

2A

N (f )W(f ) 1

T (f )

−

θθ

θ

⎛ ⎞⎜ ⎟= +⎜ ⎟⎝ ⎠

Staelin andSurussavadeeJuly 2006

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Spatial Resolution (KM) at Nadir

25252525600 rcvrs/band 0.5/D50505050300 rcvrs/band 0.5λ/D

20234651721.2-m dish(E) 0.95λ/D1214283143962-m dish(A-D) 0.95λ/D17183842581292-m dish 1.3λ/D42538018316611853

Frequency Band (GHz)Antenna type

Instrument Options Evaluated

≤ 30 km

Staelin andSurussavadeeJuly 2006

Frequencies studied for GEMApproximate Frequencies (GHz)

118.75 ±0.5, ±1.15, ±1.5, ±2.05 @ 45 km166 @ 30 km; 183.31±1, ±3, ±7, @ 25 km 380.2 ±1.5, ±4, ±9, ±18 @ 15 km 424.76 ±0.6 , ±1, ±1.5, ±4 @ 15 km

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Clear-air Incremental weighting functions (IWF) for temperature and humidity vs. offset (MHz) from line center (from Klein and Gasiewski, 2000).

Peaks of GEM/GeoSTARweighting functions analyzed here.

Note that high humidity can preclude penetration below ~2 km at 118, 166 GHz.

GEM Channel Selection Issues

−0.05 0 0.05 0.1 0.150

10

20

30

40118.7503 GHz

Altitude (

km

)

Temperature IWF (km−1)

15−21

29−41

70−90

150−250300−500500−900

900−1300← 1300−1700

← 1700−2500← 2500−3500

4000−6000↓

0 0.05 0.1 0.15 0.2 0.250

10

20

30

40424.7631 GHz

Altitude (

km

)

Temperature IWF (km−1)

25−35

60−80

120−180

250−350500−700800−12001200−1800

3500−4500

−2 0 2 4 60

5

10

15

20150−450

650−11501300−20002500−35004000−6000

← 6000−8000

15000−19000

183.3101 GHz

Altitude (

km

)

Water Vapor IWF (K km−1)

−2 −1.5 −1 −0.5 0 0.50

5

10

15

2030−60

300−500

1250−1750

3550−4450

8000−1000017000−19000↑

380.1974 GHz & 340 GHz

Altitude (

km

)

Water Vapor IWF (K km−1)

336−344 GHz

118 GHz (O2) 425 GHz (O2)

183 GHz (H2O) 380/340 GHz (H2O)

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Geo-Microwave Precipitation Retrievals

Staelin andSurussavadeeJuly 2006

Rain rate estimate R (mm/h)

118 GHz(4 O2 Channels)166-183 GHz(4 H2O Channels)380 GHz (4 H2O Channels)425 GHz (4 O2 Channels)Land/sea, elevation

R > 8? R

(mm/h)

Neural Net 2

Neural Net 3

Yes

No

8

8

8

Training (NCEP/MM5, 122 global storms)1

Nets 2 and 3 were trained with different R values (NN×1.3 better matches MM5, retrieval colors)

8Neural Net 1

(for categorization)

34

Rain-rate estimates: input = two TB spectra 15 minutes apart at 40° zenith angle. Water-path estimates are based on one spectrum (18 numbers).All networks have 10, 5 and 1 neurons in their input, hidden, and output layers,

respectively.Same general estimator architecture was used for analyzing GeoSTAR options

2

Simulations or observations

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Rain Rate and Water Path RetrievalsM

M5

Trut

hG

EM re

trie

val

Surface precipitation rate (mm/h)

Rain water path (mm)

Graupel water path (mm)

Snow water path (mm)

Retrievals: 2-m GEM antenna; 118/183/380/425-GHz bands; Front, January 2, 2003

1 2 4 8 1 2 4 1 2 4 1 2 4 8 16 32

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MM5 vs. 2-m GEM Rain Rate (mm/h)MM5 Truth 2-m GEM retrieval

European Front, 1003 UTC January 2, 2003, viewed 3 hours at 5-minute intervals

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MM5 Truth 2-m GEM retrieval

MM5 vs. 2-m GEM Rain Rate (mm/h)

Typhoon, 1625 UTC December 8, 2002, viewed 3 hours at 5-minute intervalsStaelin andSurussavadeeJuly 2006

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MM5 Truth 2-m GEM retrieval

MM5 vs. 2-m GEM Snowfall Rate (mm/h)

Moscow snow storm, 1122 UTC, March 23, 2003 Viewed for 3 hours every 5 minutes The retrieved trailing edge position is correct, the leading edge is extended

Staelin andSurussavadeeJuly 2006

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Spatial Resolution (KM) at Nadir

25252525600 rcvrs/band 0.5/D50505050300 rcvrs/band 0.5λ/D

20234651721.2-m dish(E) 0.95λ/D1214283143962-m dish(A-D) 0.95λ/D17183842581292-m dish 1.3λ/D42538018316611853

Frequency Band (GHz)Antenna type

Instrument Options Evaluated

≤ 30 km

Staelin andSurussavadeeJuly 2006

Frequenciesfor 10 Instrument Options, A-JApproximate Frequencies (GHz) A B C D E F G H I J

52.8, 53.6, 54.4, 55.5 @ 50 km • • • •118.75 ±0.5,±1.15, ±1.5, ±2.05 @ 45 km • • • • • • •166 @ 30 km; 183.31±1, ±3, ±7 @ 30/25 km • • • • • •380.2 ±1.5,±4, ±9, ±18 @ 15 km • • •424.76 ±0.6 ,±1, ±1.5, ±4 @ 15 km • • •

km72 502515

Single dish options

25 km

50

Aperture synthesis

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Representative Instrument OptionsW

arm

rain

S

tratif

orm

Typh

oon

S

trong

fron

t

Mm/hrMM5 RR 2-m GEM 1.2-m GEM 900-rcvr GS 600-rcvr GS 600-rcvr GS

118/183/380/425 118/183/380/425 54/183@50/25 km 54/118@50 km 54@25 km

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GEM vs. GeoStar’ Rain Rate Images2-m GEM 1.2-m GEM MM5 truth GS-900 (55/183) GS-600 (54/118)

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Summary and Conclusions

Staelin andSurussavadeeJuly 2006

Image sharpening can improve antenna resolution ~×1.3

Nodding subreflectors greatly reduce antenna scan momentum impact

Both 1.2- and 2-m antenna dishes could be integrated on GOES

Bands near 118, 183, 380, and 425 GHz are adequate (~16 channels)

Geostationary microwave retrievals are feasible for: - surface precipitation rates for rain and snow (mm/h), and - water paths for rain water, snow, and graupel (mm)

The simplest aperture synthesis system comparable to a 1.2-meter antenna uses 900 receivers (300 at 54-GHz, 600 at 183-GHz), each with 4 channels (high cost and risk)

No other global technique for monitoring precipitation evolution is comparable; geostationary microwave (GEM) should be part of PMM