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1、基于Landsat影像下广州市植被覆盖变化对城市热岛的影响温兴平1,2，胡光道1,2，杨晓峰31. 中国地质大学数学地质遥感地质研究所，湖北 武汉 430074；2. 地质过程与矿产资源国家重点实验室，湖北 武汉 430074；3. 南京信息工程大学环境科学与工程学院，江苏 南京 210044摘要：城市化在给人类社会带来进步的同时也给城市带来一系列环境问题，城市热岛效应是城市化进程带来的较明显的副产品。文中用1990、2000和2002年Landsat TM/ETM+遥感影像研究城市植被覆盖变化对城市热岛的影响，研究区选广州市中部七区。首先对遥感影像进行精几何校正，用支持向量机对影像进行分类并
2、计算出各区植被覆盖率。其次，用Landsat波段6反演地表亮温，计算出各区平均亮温值并转换为符合正态分布的亮温偏移值；最后对各区不同年份的植被覆盖率和亮温偏移值的关系进行研究。比较研究区3年内植被覆盖率发现，由于城市的快速发展，1990年到2000年植被覆盖率减少了7%，而2000年到2002年植被覆盖率增加了3%，区亮温偏移值与植被覆盖率呈负相关，相关系数为-0.86；比较各区不同年份亮温偏移值可以发现，越秀区的亮温偏移值在1990和2000年均高于各区，但在2002年由于该区近两年内植被覆盖率的增加而有所降低。2002年除萝岗区和白云区外，其它5区的亮温偏移值较接近，说明2002年各区的热
3、岛强度得到有效控制。关键词：植被覆盖率；亮温；城市热岛；Landsat ETM+；广州中图分类号：X16 文献标识码：A 文章编号：1672-2175（2008）03-0985-04 遥感可以在短时间内快速有效监测全球大面积地表覆盖信息，地表覆盖变化信息对于城市建设及城市规划有着重要的指导意义。城市快速发展在产生经济效益的同时也给城市环境带来一定的影响，城市热岛效应就是城市化进程中出现的较为明显的副产品。城市热岛效应是由Howard在研究英国伦敦城市气候1发现，其后便引起社会的普遍关注，目前已有大量文献研究城市热岛效应2-8。用遥感技术研究城市热岛效应具有明显的优势，首先遥感可以快速监测到大面
4、积地表覆盖信息9-11，通过比较不同时期地表覆盖信息，可以得出较准确的土地覆盖变化状况；其次利用遥感红外波段可以获得地表较高分辨率的温度分布资料2, 12, 13，这些资料用常规气象观测站是难以获取的；最后，随着卫星技术的发展，遥感影像越来越丰富，而且成本也越来越低，使利用遥感影像进行城市热岛研究更为便利。文中采用三景不同年度的Landsat影像资料来研究广州市植被覆盖变化对城市热岛的影响。研究中首先对影像监督分类得到不同年度分区植被覆盖率资料，然后用波段6进行亮温反演并对亮温进行标准化处理，最后对各区不同年度植被覆盖率变化与城市热岛之间的关系进行研究。1 研究区概况研究区位于广东省广州市，广
5、州市是广东省的省会城市，位于珠江三角洲腹地。改革开放后广州市城市发展速度很快，快速的城市发展对城市气候带来一定影响。广州市下辖十区二市，中部七区的城市热岛效应较明显，因此本研究选择中部七区（图1）为研究区，在下文中简称广州市区。图中边界为2005年调整后新的行政区边界。图1 广州市中部七区2005年调整后的行政区划Fig. 1 Guangzhou center seven districts boundary map adjusted in 20052 研究方法2.1 遥感影像分类本次研究采用Landsat三景遥感影像，分别为 图2 1990年（左）、2000（中）和2002年（右）遥感影像分
6、类Fig. 2 Classification map in 1990 (left), 2000 (middle) and 2002(right)1990年10月13日的TM影像、2000年11月1日和2002年11月7日的ETM+影像，影像采集日期较为接近，均为秋季。三景影像对应不同年份，通过对比三景影像可以得到广州市土地覆盖变化状况。研究中首先对三景影像进行精几何校正并转换到麦卡托横轴投影，将均方根误差控制在0.5个像素以内。然后用支持向量机算法14, 15对三景影像进行分类，分类结果见图2。图中不透水面指除水体、植被外的地类，包括建设区、土壤、道路等。对分类结果进行统计计算后得出，三景影像
7、水体覆盖率变化不明显，植被覆盖率从1990年到2000年期间减少7%，2000年到2002年期间增加3%。2.2 广州市区植被覆盖变化图3 广州市各区1990、2000与2002年植被覆盖率Fig. 3 Vegetation cover ratio of districts in Guangzhou in 1990, 2000 and 2002图4 广州市各区2000与1990年和2002与2000年植被覆盖率差值Fig. 4 Differential chart of districts vegetation cover ratio in Guangzhou in 1990, 2000 an
8、d 2002对三景影像分类结果进行统计分析，分区计算出不同年度植被覆盖所占的百分率。从各区植被覆盖率（图3）和植被覆盖率差值图（图4）上可以看出，多数区植被覆盖率从1990年到2000年出现大幅度下降，仅萝岗区将大片土地绿化，使植被覆盖率呈上升趋势。植被覆盖率的下降与城市快速发展有关，1990年到2000年正是广州市改革开放初期，大规模的城市化建设扩张导致植被覆盖率下降。比较2000年与2002年植被覆盖率发现，各区在2000年到2002年期间植被覆盖率均略有上升，这说明政府已开始注意到城市发展对环境带来的影响，因而加大城市绿化工作的结果。比较2000年和2002年的遥感影像可以发现，这两年内
9、，广州市区约有5%的植被覆盖区转化为建设用地，但有8%的非植被或水体用地转化为植被，总体上，广州市区在2000年到2002年两年内植被覆盖率增加约3%，其中荔湾区这两年内植被覆盖率增加最明显，增加约6%。2.3 遥感影像亮温反演 为研究土地覆盖变化与地表温度的关系，对三景影像的波段6进行亮温反演，亮温反演公式为： （1）其中：T是有效亮温，单位为K，L为辐射率，用影像DN值及影像头文件中的增益及偏移系数计算得到，单位：，K1、K2为常数，TM和ETM+影像分别采用不同系数。反演后的各区平均亮温如图5。从图上可以看出，2000年平均亮温较1990年有大幅上升，2002年较2000年有所下降，说明
10、由于植被的增加，城市热岛强度得到有效控制。1990年越秀区的平均亮温值明显高于其他各区，2002年由于植被覆盖率的增加，越秀区的平均亮温值低于1990年，说明植被覆盖率的增加可以明显减缓城市热岛效应。图5 广州市各区1990、2000与2002年平均亮温Fig. 5 Brightness temperature mean of districts in Guangzhou in 1990, 2000 and 2002通过对反演后亮温资料统计分析后发现，反演后亮温值的直方图分布接近正态分布，为比较三年内各区平均亮温值的相对变化，研究中将亮温值转化为服从正态分布的亮温偏移值，转化公式为： （2）其
11、中：i为像元序号，Zi为转换后的亮温偏移值，为市区内像元亮温的平均值，为市区像元亮温的标准差。亮温经过正态分布标准化处理后转换为亮温偏移值，一定程度上消除了部分大气及几何参数的影响，便于不同年度亮温反演资料进行比较。图6为不同年度的各区亮温偏移值的平均值。从图上可以看出，1990年越秀区的亮温偏移值最大，明显高于其他各区；2000年有所下降，2002年较2000年下降幅度最为明显，这是因为在这两年内越秀区植被覆盖率增加约5%。海珠、黄埔、荔湾在1990到2000年内由于城市建设的发展，偏移值略有上升，但2000年至2002年内由于植被覆盖度的增加，偏移值有所下降。天河区偏移值呈递增趋势，200
12、2年天河区偏移值最大。总体上，2002年广州市区城市热岛效应得到有效的控制，市内除白云、萝岗两区亮温偏移值较低外，其余五个区亮温偏移值接近。图7为植被覆盖百分率与亮温偏移值的散点图，图中为3年内七个区共21组植被覆盖率与亮温偏移值的数据。通过线性拟合后得出，各区内逐年的亮温偏移值与植被覆盖率之间的相关系数为-0.86，二者呈较强负相关，说明植被覆盖率的增加可以明显减缓城市热岛效应。图7 植被覆盖率与亮温偏移值的散点Fig. 7 Plot of vegetation cover ratio and Brightness temperature deviation value3 结论通过对广州市区
13、不同年度遥感影像进行处理，得到广州市三年的植被覆盖率及亮温反演数据，对数据分析得出如下结论：（1）1990年到2000年为广州市快速发展时期，城市的快速发展带来植被覆盖率的大幅度减小，但2000年到2002年内广州市区植被覆盖率有所回升，增加约3%。这与政府制订一系列环境保护政策有关。2002年广州市区城市热岛效应得到有效的控制，市内除白云、萝岗两区亮温偏移值较低外，其余五个区亮温偏移值接近。（2）亮温偏移值与植被覆盖率呈明显负相关，相关系数为-0.86，植被覆盖率的提高可明显减缓热岛效应。1990年越秀区的亮温偏移值最大，2000年有所下降，2002年较2000年下降幅度最为明显，这是因为在
14、这两年内越秀区植被覆盖率增加约5%。图6 广州市各区1990、2000与2002年平均亮温偏移值Fig. 6 Brightness temperature deviation mean value of districts in Guangzhou in 1990, 2000 and 2002参考文献：1 HOWARD L. The climate of London, deduced from meteorological observationsM. 3rd ed. Vol.1. London: Harvey and Darton, 1833: 1-348.2 CHEN X L, ZHAO
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22、 PAOLINI L. Land surface temperature retrieval from LANDSAT TM 5J. Remote Sensing of Environment, 2004, 90(4): 434-440.14 SCHOLKOPF B, SUNG K K, BURGES C J C, et al. Comparing support vector machines with Gaussian kernels to radialbasis function classifiersJ. Signal Processing, IEEE Transactions on,
23、 1997, 45(11): 2758-2765.15 SU L, CHOPPING M J, RANGO A, et al. Support vector machines for recognition of semi-arid vegetation types using MISR multi-angle imageryJ. Remote Sensing of Environment, 2007, 107(1-2): 299-311.The Effect of Vegetation Cover Change on Urban Heat Island in Guangzhou Using
24、Landsat ImagesWen Xingping1,2, Hu Guangdao1,2, Yang Xiaofeng31. Institute of Mathematic Geology and Remote Sensing Geology, China University of Geosciences, Wuhan 430074, China;2. State Key Laboratory of Geological Processes and Mineral Resources, Wuhan 430074 China;3. College of Environmental Scien
25、ce and Engineering, Nanjing University of Information Science & Technology, Nanjing 210044, ChinaAbstract: Urbanization makes progress in human society, at the same time it brings a series of environmental issues to city. The urban heat island effect is one of the obvious byproducts brought by urban
26、ization. In this paper, the effect of vegetation cover change on urban heat island is investigated using three Landsat TM/ETM+ images acquired in 1990, 2000 and 2002. The study area is located at the centre seven districts of Guangzhou city, in China. Firstly, the images were geometric precision cor
27、rection and classified using Support Vector Machine (SVM), and then every district vegetation cover ratio was computed out. Secondly, brightness temperature was retrieved by band 6, and the brightness temperature mean of every district was computed out and converted into the deviation value which be
28、longed to normal distribution. Finally, the relationship between vegetation cover ratio and the brightness temperature deviation value in different years was investigated. Comparing three years vegetation cover ratio of study areas, it concludes that the vegetation cover ratio was decreased by 7% fr
29、om 1990 to 2000 due to the city rapidly development, however, it increased 3% from 2000 to 2002. The district brightness temperature deviation mean value was positively correlated with the vegetation cover ratio and the correlation coefficient is -0.86. Comparing districts brightness temperature dev
30、iation mean value in different years, the brightness temperature deviation mean value of Yuexiu District is the highest in 1990. However, it decreased in 2002 due to the vegetation cover ratio increase in the last two years. In 2002, all districts have the near brightness temperature deviation mean
31、value except Luogang and Baiyun, so the difference of heat island intensity between districts is not significant.Key words: vegetation cover ratio; brightness temperature; urban heat island; Landsat ETM+; GuangzhouEditors note: Judson Jones is a meteorologist, journalist and photographer. He has fre
32、elanced with CNN for four years, covering severe weather from tornadoes to typhoons. Follow him on Twitter: jnjonesjr (CNN) - I will always wonder what it was like to huddle around a shortwave radio and through the crackling static from space hear the faint beeps of the worlds first satellite - Sput
33、nik. I also missed watching Neil Armstrong step foot on the moon and the first space shuttle take off for the stars. Those events were way before my time.As a kid, I was fascinated with what goes on in the sky, and when NASA pulled the plug on the shuttle program I was heartbroken. Yet the privatize
34、d space race has renewed my childhood dreams to reach for the stars.As a meteorologist, Ive still seen many important weather and space events, but right now, if you were sitting next to me, youd hear my foot tapping rapidly under my desk. Im anxious for the next one: a space capsule hanging from a
35、crane in the New Mexico desert.Its like the set for a George Lucas movie floating to the edge of space.You and I will have the chance to watch a man take a leap into an unimaginable free fall from the edge of space - live.The (lack of) air up there Watch man jump from 96,000 feet Tuesday, I sat at w
36、ork glued to the live stream of the Red Bull Stratos Mission. I watched the balloons positioned at different altitudes in the sky to test the winds, knowing that if they would just line up in a vertical straight line we would be go for launch.I feel this mission was created for me because I am also
37、a journalist and a photographer, but above all I live for taking a leap of faith - the feeling of pushing the envelope into uncharted territory.The guy who is going to do this, Felix Baumgartner, must have that same feeling, at a level I will never reach. However, it did not stop me from feeling his
38、 pain when a gust of swirling wind kicked up and twisted the partially filled balloon that would take him to the upper end of our atmosphere. As soon as the 40-acre balloon, with skin no thicker than a dry cleaning bag, scraped the ground I knew it was over.How claustrophobia almost grounded superso
39、nic skydiverWith each twist, you could see the wrinkles of disappointment on the face of the current record holder and capcom (capsule communications), Col. Joe Kittinger. He hung his head low in mission control as he told Baumgartner the disappointing news: Mission aborted.The supersonic descent co
40、uld happen as early as Sunday.The weather plays an important role in this mission. Starting at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. The balloon, with capsule attached, will move through the lower level of the
41、atmosphere (the troposphere) where our day-to-day weather lives. It will climb higher than the tip of Mount Everest (5.5 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratosphere. As he crosses the boundary l
42、ayer (called the tropopause), he can expect a lot of turbulence.The balloon will slowly drift to the edge of space at 120,000 feet (22.7 miles/36.53 kilometers). Here, Fearless Felix will unclip. He will roll back the door.Then, I would assume, he will slowly step out onto something resembling an Ol
43、ympic diving platform.Below, the Earth becomes the concrete bottom of a swimming pool that he wants to land on, but not too hard. Still, hell be traveling fast, so despite the distance, it will not be like diving into the deep end of a pool. It will be like he is diving into the shallow end.Skydiver
44、 preps for the big jumpWhen he jumps, he is expected to reach the speed of sound - 690 mph (1,110 kph) - in less than 40 seconds. Like hitting the top of the water, he will begin to slow as he approaches the more dense air closer to Earth. But this will not be enough to stop him completely.If he goe
45、s too fast or spins out of control, he has a stabilization parachute that can be deployed to slow him down. His team hopes its not needed. Instead, he plans to deploy his 270-square-foot (25-square-meter) main chute at an altitude of around 5,000 feet (1,524 meters).In order to deploy this chute suc
46、cessfully, he will have to slow to 172 mph (277 kph). He will have a reserve parachute that will open automatically if he loses consciousness at mach speeds.Even if everything goes as planned, it wont. Baumgartner still will free fall at a speed that would cause you and me to pass out, and no parach
47、ute is guaranteed to work higher than 25,000 feet (7,620 meters).It might not be the moon, but Kittinger free fell from 102,800 feet in 1960 - at the dawn of an infamous space race that captured the hearts of many. Baumgartner will attempt to break that record, a feat that boggles the mind. This is one of those monumental moments I will always remember, because there is no way Id miss this.
