| 1. | Cloud detection and analysis of modis image
图象的云检测及分析 |
| 2. | Cloud detection radar
测云雷达 |
| 3. | Experimental results showed that the method can get a higher precision for cloud detection
试验结果表明，该方法能够取得较高的云检测精度。 |
| 4. | This paper presents two methods for cloud detection : multi - channel dynamical threshold algorithm and apparent reflectance algorithm
本文介绍了两种云检测算法：双通道动态阈值法和表观反射率法。 |
| 5. | Finally , the modis cloud detection results are used as validation for both algorithms tested with gms5 images in this research
最后用modis的云检测结果对双通道动态阈值法和表观反射率法分别进行真实性检验。 |
| 6. | The apparent reflectance algorithm estimates the clear - sky visible apparent reflectance as the bases of visible channel thresholds with the 6s radiation transfer model . cloud detection is tested with apparent reflectance algorithm to gms5 images
将表观反射率乘以不同的系数得阈值，待检测云图的表观反射率大于阈值的像元为云像元。 |
| 7. | Based on judge whether the visual band was valid or not , the method separated land region from water region , and then set proper threshold values separately for land and water regions in different images and different bands , by that way an automatic cloud detection could be achieved
该方法在可见光波段是否有效判断的基础上，进行图像水陆区域划分，然后对不同图像、不同波段的水域和陆域分别设定合理的阈值，实现了云自动检测目的。 |
| 8. | The cloud detection results are also compared with control masks that are created by visual inspections . in case the multi - day clear - sky composition is contaminated by cloud cover , it adds the chance of clear score failure . in case the multi - day clear - sky composition there is no snow cover , but in the same area at the image for detection there is snow , it also adds the chance of clear score failure
用表观反射率法对gms5云图进行云检测，如果晴空合成图某区域有云覆盖，则易将被检测的云图相应区域的云误判成地表，如果某个区域的晴空合成图没有雪覆盖，而被检测云图该区域有雪覆盖，则必将雪误判成云。 |
| 9. | Main conclusions drawn from the analyses of calculating results are as follows : ( 1 ) the microwave absorption of atmosphere gas have obvious attenuation at the wavelengths for cloud detection , thereinto , the water attenuation effect changes greatly , so the 94ghz cloud detecting radar should have water vapor attenuation correction scheme . ( 2 ) when 37ghz and 94ghz radars detect clouds , the difference between the atmosphere and cloud attenuation and the large variety of radar reflectivity conduce the intension of the radar backscatter signals change . ( 3 ) for the thin cloud layer and low water content of cloud , 37 - ghz radar backscatter signals are not as good as 94 - ghz radar , that is to say that the 94ghz radar has better capability in thin clouds detection
本工作得出如下结论： ( 1 )大气气体的微波吸收在测云波段产生明显的衰减，其中水汽衰减效应变化很大；即将上天的空间94ghz测云雷达必须有水汽衰减订正方案； ( 2 ) 37ghz和94ghz雷达测云，由于大气和云衰减不同和雷达反射率的很大差异，导致雷达回波信号强弱不同； ( 3 )对云层较薄、含水量较少的云，在不计雷达参数的情况下， 37ghz雷达回波信号不如94ghz测云雷达，也就是说94ghz对薄云有更强的探测能力；对云层较厚、含水量大的云，由于强衰减的作用， 94ghz雷达回波信号小于37ghz雷达； ( 4 )从大气衰减的不利因素方面考虑，空间94ghz雷达测高层薄云的效果最好；测低层薄云时需要考虑气体衰减订正；因浓厚云的强衰减作用，探测其中下部的能力大大减弱，不仅要进行衰减订正，而且要借助其他信息来反演整个云层的含水量垂直分布； （ 5 ）为了获得从极薄到极浓厚云的垂直分布探测能力，未来测云雷达系统最好采用双波长甚至三波长（如94 、 37和13ghz ） 。 |
