# Presentation: 247793

## GV for Taiwan’s precipitation retrieval research 

- Wann-Jin Chen
- Chung Cheng Institute Technology of National Defense University, Taiwan

## Outline

- Introduction
- Estimates of Rainfall using TMI data  over the Ocean during Mei-Yu and Typhoon season
- Estimates of Rainfall using TMI data  over the Land during Mei-Yu and Typhoon season
- Ground Validation
- Future work

## Two Heavy rainfall Season

- Mei-Yu (Meso-scale convective systems), occurred during May and June.
- Typhoon occurred during August through October.
- Many natural disasters in Taiwan areas caused by the two weather systems, so the following studies were focused  on them.

## Estimates of Rainfall using TMI data  over the Oceanduring Mei-Yu season

## Methodology

- Match-up with TMI_Tb and Rain Gauge

- The regression of Multichannel during Mei-Yu season

##                 Typhoon SINLAKU

- TMI-2002-09-05_1407

- GMS-2002-09-05_1400

-                 Typhoon SINLAKU

## Quantification Validation during 

**Mei-Yu season**

- 1998~2001
- 18 points
- R2= 0.812

## Estimates of Rainfall using TMI data  over the Oceanduring Typhoon season

## The regression over ocean

| 
Rain Type |              
Regression Equation | 
Correlation Coefficient (R) |
| --- | --- | --- |
| 
Convective precipitation  | RR19s=152.65-0.77*Tb1+0.47*Tb2- 
              0.147*Tb3+0.537*Tb4
               -0.508*Tb5+0.818*Tb6-
               0.773*Tb7-
               0.91*Tb8+0.803*Tb9  |  

0.85 |
| 
Stratiform precipitation | RR19a=-44.28-0.107*Tb1+0.06*Tb2+0.7*
             Tb3-0.15*Tb4-
             0.308*Tb5+0.148*Tb6-
             0.15*Tb7-0.17*Tb8+0.18*Tb9 |  

0.5 |

- Rainfall Rate (mm/hr)
-  by Regression.
- #37769  (this study)
- Typhoon** MINDULLE**

- Rainfall Rate
-  (mm/hr) by 2A12.

- Delta Rainfall Rate (mm/hr).

## Validation

**R=0.74, RMS=3.75 mm/hr, Bias: 0.68 (1.24%) , Points=66 (CO:25, ST:41)**

**CO :****● Convective**
**ST : ****+ ****Stratiform**

**Average Rain Rate of **
**Rain Gauge : 4.9 mm/hr.**
**Average Rain Rate of**
** ****Estimated : 5.6 mm/hr.**

## Validation (2A12)

**R**** ****=0.45, RMS=5.76 mm/hr, Bias=2.52 (-0.29%), Points: 66**

## Estimates of Rainfall using TMI data  over the Landduring Typhoon season

## Data Collection

- The  illustration is a scatter of ground rain gauge in Taiwan

- The scan patterns and resolutions of TRMM sensors, including TMI, PR, and VIRS.

## Scattering Index over Land( SIL ) Equation

**Developing Scattering Index over Land( SIL ) equation for Taiwan land area.**
**Using TRMM/TMI 19.35V, 21.3V and 85.5V GHz channel.**
**Under non-scattering atmosphere conditions, that identified weather as cloud-free on Taiwan region with GOES-9 IR images.**

## TMI data set used in the study. 

| NO. | DATE | TIME(UTC) | Orbit # |
| --- | --- | --- | --- |
| 1 | 2004/06/30 | 12:20 | #37758 |
| 2 | 2004/07/01 | 04:52 | #37769 |
| 3 | 2004/07/01 | 11:24 | #37773 |
| 4 | 2004/07/02 | 05:35 | #37785 |
| 5 | 2004/07/02 | 12:07 | #37789 |

## The Rainfall Retrievals over Land 
The scatter diagrams of the SIL and Gauge Rain rate

**The scatter diagrams of the SIL and Gauge Rain rate**

- RR(rain rate) = 0.126  SIL 1.239

- Sample:74

- SIL(K)

- Gauge Rain rate (mm/hr)

## *LRCT(Land Rainfall Retrieval by Chen and Tsai) 

| Ferraro et al.(1994)   for global rainfall retrieval |
| --- |
| SIL = 451.9–0.44(Tb19V)–1.775( Tb22V )+0.00575( Tb22V )2-Tb85V  |
| RR ( mm/hr ) = 0.00513 ( SIL 1.9468  )  |
|  |
| LRCT*(2005)   for Taiwan’s local areas |
| SIL=220.878–0.747(Tb19V)+0.554(Tb21V)+0.00147(Tb21V)2–Tb85V  |
| RR ( mm/hr ) = 0.126 ( SIL 1.239 )  |

- *LRCT(Land Rainfall Retrieval by Chen and Tsai)

##  Validating the Accuracy of Estimated  Rainfall over land _Typhoon AERE  (sample:23)

| Methords of Rainfall Retrievals |  | Mean value
 ( mm/hr ) | BIAS
 ( mm/hr ) | RMS 
( mm/hr ) |
| --- | --- | --- | --- | --- |
| LRCT
(2005) | ground truth   | 5.53 | 0.56
(10%)
 | 3.48 |
|  | estimated rainfall | 6.10 |  |  |
| Ferraro
(1994) | ground truth  | 5.53 | -2.82
(-51%) | 4.28 |
|  | estimated rainfall | 2.71 |  |  |

## Validating the Accuracy of Estimated Rainfall over land _Typhoon MINDULLE (sample:74)

| Methords of Rainfall Retrievals |  | Mean value 
( mm/hr ) | BIAS
 ( mm/hr ) | RMS
 ( mm/hr ) |
| --- | --- | --- | --- | --- |
| LRCT | ground truth   | 14.15 | -0.01
(-0.07%)
 | 5.14 |
|  | estimated rainfall | 14.14 |  |  |
| Ferraro
(1994) | ground truth  | 14.15 | -4.82
(-34%) | 7.13 |
|  | estimated rainfall | 9.33 |  |  |

## Error analysis : time difference

- Satellite rainfall retrievals have a good result when comparing with rain gauge with 10 min. later after satellite overpass for the Mei-Yu cases.

## Over the land _ Mei-Yu

|  |  |     - 60 min |  - 50 min |  - 40 min | - 30 min | - 20 min | - 10 min |
| --- | --- | --- | --- | --- | --- | --- | --- |
| RMS | May | 8.7 | 8.9 | 8.33 | 7.86 | 8.17 | 7.48 |
|  | June | 7.01 | 6.7 | 7.42 | 6.71 | 6.15 | 6.05 |
| Correlation
 Coefficient | May | 0.19 | 0.3 | 0.35 | 0.41 | 0.41 | 0.48 |
|  | June | 0.47 | 0.55 | 0.49 | 0.55 | 0.57 | 0.58 |
|  |  |  |  |  |  |  |  |
|  |  |  |  |  |  |  |  |
|  |  | same time |  +10 min |  +20 min | +30 min | +40 min | +50 min |
| RMS | May | 7.22 | 6.72 | 7.1 | 7.2 | 7.78 | 8.04 |
|  | June | 5.86 | 6.25 | 6.5 | 6.6 | 6.98 | 7.09 |
| Correlation
 Coefficient | May | 0.54 | 0.6 | 0.55 | 0.52 | 0.45 | 0.4 |
|  | June | 0.61 | 0.57 | 0.53 | 0.52 | 0.46 | 0.45 |

- Validating the Accuracy of Estimated Rainfall with QPESUMS Data ( -/+: before/after satellite overpass)

## RMS

**June**

**May**

| -60 | -50 | -40 | -30 | -20 | -10 | 0 | +10 | +20 | +30 | +40 | +50 |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |

- ( -/+: before/after satellite overpass ; ‘0’: same time )

## Correlation Coefficient

**June**

**May**

| -60 | -50 | -40 | -30 | -20 | -10 | 0 | +10 | +20 | +30 | +40 | +50 |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |

- ( -/+: before/after satellite overpass ; ‘0’: same time )

## The scatter diagrams of the estimated rainfall and  the Gauge Rain rate 

- Rainfall Retrievals derived from LRCT(2005)  (left), Ferraro (1994) (right)
- ( Black solid line is the regression line between Est.-RR and rain gauge RR, and the red solid line is for the equivalent values between them. )

- Correlation Coefficient :0.82

- Correlation Coefficient :0.81

## Error analysis : terrain effect

- Satellite rainfall retrieval underestimated on upsloping side of the mountain and overestimated on the downsloping side of the mountain.

## Future works

- Improve rain gauge QC.
- Develope more algorithms for other weather systems in Taiwan area.
- Use more passive microwave radiometer sensors, like AMSR, AMSU in our algorithm.
-  Compare satellite rainfall retrievals with those derived from ground-based radar.

## The End !Thanks for your attention!