Precipitation Remote Sensing

Precipitation Remote Sensing

Huade Guan

Prepared for Remote Sensing class Earth & Environmental Science University of Texas at San Antonio

November 14, 2005

Outline

• Background

• Remote sensing technique for estimating precipitation, and related sensors

• NEXRAD

• Testing and improving NEXRAD products

• Future mission

http://www.uwsp.edu

Precipitation physics

http://eesc.columbia.edu/courses/ees/slides/climate/

Precipitation physics

www.gc.maricopa.edu

http://www.synthstuff.com/mt/archives/flickr-lenticular-cloud.jpg

http://www.uwsp.edu/geo/faculty/lemke/geog101/lecture_outlines/08_precipitation_processes.html cold front

warm front

Occluded front

http://rsd.gsfc.nasa.gov/rsd/images/Georges/GeorgesMS_md.jpg

Precipitation processes

http://www.uwsp.edu

http://www.mvinstitute.org

http://www.usatoday.com/weather/wtipgage.htm

http://www.hubbardbrook.org/yale/watersheds/w6/rain-gauge-stop/precipitation.htm

Gauge

measurement

Problems of gauge measurement:

1) Limited spatial coverage 2) …

Four types of mapping approaches

(examples)

Spatial covariance

Information incorporated

No Yes

No Theissen polygon,

& inverse square distance

Kriging Physical process

Yes Regression, e.g., P-Z

Cokriging (P-Z)

& De-trended residual kriging

Precipitation remote sensing

• Satellite-based

– Geostationary (e.g., GOES)

– Polar orbiting (e.g., AVHRR, TRMM)

• Ground-based

– NEXRAD

VIS/IR technique

• Outgoing Longwave Radiation

– Basis: Precipitation leading to outgoing longwave radiation different from normal background

– Empirical relationship: P~OLR

– Example: IR bands of AVHRR or NOAA-series satellites for OLR, explained 40% of the areally average rainfall variability.

VIS/IR technique

• GOES Precipitation Index (GPI)

– Basis: cold cloud-top temperature leads to precipitation

– For pixels of cloud-top temperature (CCTs) less than 235 K are classified as raining pixel, and assigned a rainfall rate of 3 mm/hr

– Reproduce climate-scale precipitation patterns for tropics and sub-tropics

– But problematic for orographic and high-latitude precipitation

VIS/IR technique

• Bristol Algorithms (e.g., PERMIT: Polar-Orbiter Effective Rainfall Monitoring Integrative Technique)

– “rain days” based on the threshold IR brightness temperature – Spatially variable mean-rain-per-day (from other sources)

• RAINSAT

– Use both visible and near-infrared

– Trained the model using radar observations

• PERSIANN Products based on GOES infrared brightness temperature

http://hydis8.eng.uci.edu/persiann/

Passive microwave technique

• Basis: precipitation-size ice particles and raindrops can scatter microwave and reduce the bulk emissivity of the cloud.

• 85.5 GHz brightness temperature

• SSM/I algorithms

– Empirical relationship

RADAR technique

http://www.everythingweather.com/weather-radar/principles.shtml

TRMM RADAR

• TRMM PR sensor

– uses radar frequencies of 13.796 and 13.802 GHz

– horizontal resolution = 4.3 km at nadir

– measurements sensitivity better than 0.5 mm/h

– measures rain from the

ground to an altitude of 15 km a vertical ("range")

resolution of 250 m.

– provides 3-dimensional rainfall distribution

Nex Nex t Generation Weather t Generation Weather Rad Rad ar WSR ar WSR - - 88D ( 88D ( NEXRAD NEXRAD ) )

http://www.everythingweather.com/weather-radar/principles.shtml

Standard Standard Z = 300 R Z = 300 R

Tropical Tropical

Z = 250 R Z = 250 R

Unit!

160 Radars

First deployed: in 1988

Wavelength: 10cm

Spatial Resolution (km): ~ 4

Temporal Resolution: 6-10 minutes

The radar will complete one volume scan (nine elevation scans) every six minutes.

The radar will complete one volume scan (14 elevation scans) every five minutes

Virga effect, range degradation

and beam blockage

http://apollo.lsc.vsc.edu/classes/remote/lecture _notes/radar/conventional/bright_band.html

Bright band contamination

http://grappa.meteo.mcgill.ca/bright_band.html

NEXRAD rainfall products NEXRAD rainfall products

(4 km and hourly) (4 km and hourly)

• • Stage I - Hourly digital precipitation (HDP) Stage I

• • Stage II - HDP merge with gauges Stage II

• • Stage III - Mosaicked Stage II cover a RFC area Stage III or MPE (

• • Stage IV Stage IV

- Mosaicked Stage III / MPE for continental U.S.

(Richard Fulton, Dong-Jun Seo, Jay Breidenbach, 2002)

Stage III/MPE Stage III/MPE

in 13 RFCs in 13 RFCs

http://dipper.nws.noaa.gov/hdsb/data/nexrad/wgrfc_stageiii.html

DATABASE and Visualization

Data can be downloaded: ftp://[email protected]/

ArcIMS HTML viewer and JAVA viewer

NEXRAD rainfall NEXRAD rainfall

products testing

products testing

A physically based parsimonious A physically based parsimonious approach (ASOADeK) for NEXRAD approach (ASOADeK) for NEXRAD

rainfall downscaling rainfall downscaling

4km 4km Æ Æ 1km 1km

Physical process (1)

Orographic effects on precip.

P (low Z) < P( high Z) wind T↓

T↑

Elevation (Z)

P (windward) > P( leeward)

Orographic lifting, & hindrance Reduction in virga effect

P (low Z) < P( high Z) We use cos (

α

ω

approximate terrain aspect effects wind

direction:

ω

terrain

aspec t: α

terrain

aspect

Physical process (2)

Atmospheric effects on precipitation

How does this heterogeneous atmospheric moisture distribution (or gradient in atmospheric moisture) influence precipitation?

We use geographic coordinates (Longitude or X, and Latitude or Y) to capture the effect of gradient in atmospheric moisture on

precipitation

GOES East 4-km, infrared imagery 2001.05.04

Study area May Precip. Map

Auto-search orographic and atmospheric effects

) cos(

...

2 1

0

+ + + + + α − ω

= b b X b Y b Z b P

aspect

moist. flux dir. Regression:

gradient in moist., elevation, aspect & moist. flux direct.

Data: Gauge precip: X, Y, P; Elev. DEM: X, Y, Z,

α

But what about moisture flux direction,

ω

6 4

5 4

sin cos

:

sin sin

cos cos

) cos(

b b

b b

Let

=

=

+

=

−

ω ω

ω α

ω α

ω

α

Future … Future …

GPM's two instruments:

• Dual-frequency Precipitation Radar (DPR), and

• the GPM Microwave Imager (GMI)

Supersite

Regional Raingauge Site Both Supersite &

Raingauge Site

Australia NASA Ocean Japan South Korea

India France (Niger-Benin)

Italy Germany

Brazil

England Spain NASA KSC NASA Land

Canada

Taiwan

Meteorology-Microphysics Aircraft GPM Primary Satellite

Radar/Radiometer Prototype Instruments Piloted

UAVs

Ground

Ground

validation

validation