Use of Representative Pixels of Motion for Wind Vector Height Assignment of Semi-transparent Clouds

Zhang Xiaohu; Zhang Qisong; Xu Jianmin

doi:10.11898/1001-7313.20170302

Vol.28, NO.3, 2017

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Article Navigation > Journal of Applied Meteorological Science > 2017 > 28(3): 270-282

Zhang Xiaohu, Zhang Qisong, Xu Jianmin. Use of representative pixels of motion for wind vector height assignment of semi-transparent clouds. J Appl Meteor Sci, 2017, 28(3): 270-282. DOI: 10.11898/1001-7313.20170302.

Citation:

Zhang Xiaohu, Zhang Qisong, Xu Jianmin. Use of representative pixels of motion for wind vector height assignment of semi-transparent clouds. J Appl Meteor Sci, 2017, 28(3): 270-282. DOI: 10.11898/1001-7313.20170302.

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Use of Representative Pixels of Motion for Wind Vector Height Assignment of Semi-transparent Clouds

DOI: 10.11898/1001-7313.20170302

National Satellite Meteorological Center, Beijing 100081

Received Date: 2016-12-13
Rev Recd Date: 2017-04-10
Publish Date: 2017-05-31

Abstract

Abstract

Height assignment of semi-transparent clouds needs two variables:Radiation from semitransparent clouds themselves and radiation from the background underneath semitransparent clouds. Generally, the former radiation is calculated using algorithms based on all pixels in tracer boxes. A new algorithm, however, is proposed considering only pixels with great contribution to correlation coefficients during wind vector tracing stage, and only allow these pixels to join the calculation. Scatter diagrams are made with infrared brightness temperature against their contribution to the feature tracking correlation coefficients. Scatter diagrams show a "C" shape pattern and can be used to recognize representative pixels of motion. Pixels with relative less contribution to correlation coefficients are at the left side of the "C" shape with infrared brightness temperature in the middle range. The other pixels with relative more contributions are naturally separated into two branches with warmer and colder infrared brightness temperature respectively. When tracer boxes are partly covered by clouds, the warm branch pixel brightness temperature is with typical ground feature at both the scope and the variability. And when tracer boxes are totally covered by clouds, warm branch pixels are in the slot of clouds with typical cloud features among cloud cells. Thus, no matter tracer boxes are partly covered or totally covered by clouds, cold branch pixels with greater contribution to correlation coefficients are better at representing the cloud motion and can be named as pixels with contribution to the motion. The algorithm using different pixel's contribution to the feature tracking improves height assignment quality by effectively removing rapid changing pixels in tracer boxes when estimating the cloud height. Using representative pixels of motion at the estimation of radiation from semi-transparent clouds themselves, FY-2 wind vector height assignment quality is improved.
- wind vector;
- height assignment;
- pixels representative of motion

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References(22)

Figures and Tables

Fig. 1 Schematic diagram of the algorithm of semi-transparent cloud height estimation

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Fig. 2 Typical examples for the tracer partly covered by clouds (a) tracer box located at 30.94°N, 120.44°E, (b) tracer box located at 15.86°N, 118.81°E, (c) tracer box located at 33.41°N, 123.83°E

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Fig. 3 Typical examples for the tracer totally covered by cloud (a) tracer box located at 34.56°N, 112.82°E, (b) tracer box located at 6.27°N, 139.42°E, (c) tracer box located at 5.33°N, 93.30°E, (d) tracer box located at 2.42°N, 90.35°E, (e) tracer box located at 29.27°S, 97.89°E

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Fig. 4 Diagram of pixel number ratio and pixel mean contribution ratio between warm and cold segments

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Fig. 5 Histogram of total contribution ratio between warm and cold segments

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图 6 暖区段和冷区段像元数之比直方图

(a) 暖区段和冷区段总贡献之比小于0.3，(b) 暖区段和冷区段总贡献之比为0.8~1.2，(c) 暖区段和冷区段总贡献之比大于2

Fig. 6 Histogram of pixel number ratio between warm and cold segments

(a) total contribution ratio between warm and cold segments less than 0.3, (b) total contribution ratio between warm and cold segments in 0.8-1.2, (c) total contribution ratio between warm and cold segments greater than 2

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图 7 追踪图像块中最高红外亮温的直方图

(a) 暖区段和冷区段总贡献之比小于0.3，(b) 暖区段和冷区段总贡献之比为0.8~1.2，(c) 暖区段和冷区段总贡献之比大于2

Fig. 7 Histogram of IR maximum temperature in tracer boxes

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Table 1 Bias and standard deviations between FY-2E wind vectors and ECMWF analyses for height assignment algorithms whether using contribution to the motion

统计量	未使用代表运动像元	使用代表运动像元
偏差/(m·s^-1)	-4.239	-2.103
标准差/(m·s^-1)	7.787	7.436
风矢量数	13895	13536

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