Statistical Model and Estimation of Inland Riverine Turbidity with Landsat 8 OLI Images: a Case Study
Total Page:16
File Type:pdf, Size:1020Kb
ENVIRONMENTAL ENGINEERING SCIENCE ORIGINAL ARTICLE Volume 00, Number 00, 2017 ª Mary Ann Liebert, Inc. DOI: 10.1089/ees.2016.0540 Statistical Model and Estimation of Inland Riverine Turbidity with Landsat 8 OLI Images: A Case Study Xin Shen1–3 and Qi Feng,4,5,* 1State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing, Wuhan University, Wuhan, China. 2Collaborative Innovation Center of Geospatial Technology, Wuhan, China. 3School of Resources and Environmental Sciences, Wuhan University, Wuhan, China. 4Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan, China. 5Key Laboratory for Environment and Disaster Monitoring and Evaluation, Hubei, China. Received: October 27, 2016 Accepted in revised form: May 25, 2017 Abstract The Landsat 8 Operational Land Imager (OLI) was investigated for its performance in monitoring dynamic riverine surface water turbidity. China’s Hanjiang River, the largest tributary of the Yangtze River, was used as a case study. Field surveys conducted between April 2013 and January 2014 show a wide range of turbidity (15.8–130.2 nephelometric turbidity units). A practical exponential retrieval algorithm used in conjunction with OLI bands on Landsat 8 was developed to assess compatibility between satellite remote sensing reflectance and in situ measured data. Results obtained for the study area accurately match in situ data at most stations (R2 > 0.90) for the validation phase. It was found that Landsat 8 OLI imagery can be used to estimate turbidity in inland riverine systems when a suitable retrieval algorithm is applied. In addition, algal blooms in the riverine system can be detected by OLI imagery. Keywords: algae bloom; Landsat 8; Hanjiang River; riverine systems; turbidity Introduction with high spectral resolution and sensitivity, which makes them suitable for studies of some inland water bodies such as urbidity (Tur) is considered a key water quality vari- large lakes or reservoirs (Shi et al., 2014, 2015; Zhang et al., able due to its impact on light suppression, biochemical T 2016a), their spatial resolution is typically too coarse to ad- oxygen demand, sediment-associated contaminant transport, equately investigate riverine features, making them unsuit- and suspended sediment loads, which affect organisms and able for monitoring water quality variations in these systems inland riverine habitats (Lawler et al., 2006; Davies-Colley (Ghabavati et al., 2008; Onderka and Peka´rova´, 2008; Yu et al., 2011; Jones et al., 2012). Owing to unique optical et al., 2012). properties of turbidity, this parameter can be estimated from Landsat sensors, such as the Landsat 5 (Thematic Mapper) remotely sensed data, thus achieving wide spatial and tem- and Landsat 7 (Enhanced Thematic Mapper Plus), may have poral coverage compared with traditional sampling methods longer revisit times and lower spectral and radiometric res- (Simis et al., 2007; Guttler et al., 2013). olution than ocean-specific instruments, but possess higher Well-established algorithms for recurrent ocean sensor spatial resolution. Accordingly, those sensors have been used monitoring of turbidity exist, employing reflectance in the for inland water studies (Vincent et al., 2004; Ma et al., blue and green color regions of oceans (Gordon and Franz, Onderka and Peka´rova´, 2008; Kuster, 2012). 2008; Neukermans et al., 2012). However, these algorithms After the retirement of Landsat 5, the failure of Landsat 6, may not be appropriate for inland water systems such as and limitations with Landsat 7, the Landsat 8 satellite was rivers due to differing optical properties of sea water bodies Downloaded by University of Connecticut e-journal package NERL from online.liebertpub.com at 07/05/17. For personal use only. launched on February 11, 2013, and operations began on May (Le et al., 2011; Yacobi et al., 2011; Li et al., 2012). Al- 30 of the same year. With its nine bands, Landsat 8 imagery though some ocean color sensors possess short revisit times provides sufficient spatial resolution, in which features such as islands within rivers and bridges spanning rivers can be easily distinguished as highly reflective structures before a *Corresponding author: Key Laboratory for Environment and Disaster Monitoring and Evaluation, Hubei, China. Phone: +86- dark background (Vanhellemont and Ruddick, 2014). Com- 027-6888-1075; Fax: +86-027-6888-1362; E-mail: fengqi@asch pared with previous Landsat missions, Landsat 8 also offers .whigg.ac.cn higher signal-to-noise ratios. This is primarily the result of 1 2 SHEN AND FENG longer integration times associated with the push broom readily available imagery from Landsat 8 together with scanner as well as improved quantization (NASA, 2016; published literature to assess water turbidity changes in the USGS, 2016). Because of inclusion of the Operational Land inland riverine system. Imager (OLI), Landsat 8 has the potential to become the first Landsat sensor with the radiometric resolution necessary for Study Area and Data Processing retrieval of chlorophyll and suspended material constituents Study area in oceans and lakes (Gerace et al., 2013; Pahlevan and Schott, 2013; Wu et al., 2015; Zhang et al., 2016b). However, few The Hanjiang River (historically called the Hanshui River) studies have applied Landsat 8 images to retrieve riverine is a major tributary of the Yangtze River and has a total length water quality parameters. of 1,577 km. The river originates in the mountainous region Rapid economic development and anthropogenic activity of southwestern Shaanxi and flows eastward across the in and around Hanjiang River have increased ecological southern expanse of the province. The Qin Mountains are pressure on its water quality, which is of great environ- north of the mouth of the river. Further north is the Wei River, mental importance to Hubei Province (Liu and Yu, 1992; the largest tributary of the Yellow River, which forms the Wang et al., 2004; Guo et al., 2014). In addition, the Dan- southern boundary of the Ordos Loop. The Daba Mountains to jiangkou Dam, which is on the upstream of the Hanjiang the south of the river act as a natural boundary that separates River and was originally constructed in 1958, has since Shaanxi Province from Sichuan Province and Chongqing City. been raised, and the Danjiangkou Reservoir, created by the The river flows southeastward through Hubei Province, construction of Danjiangkou Dam, has been used as part of connecting with the Yangtze River at Wuhan, the provincial the South-to-North Water Diversion Project (SNWDP) since capital. 2014. Research has shown the probability that algal blooms In the study area (Fig. 1), the main cities along the Han- will increase in the mid-downstream region of the Hanjiang jiang River are Qianjiang City (population 1.1 million) to the River after completion of the SNWDP (Xie et al., 2004). west and Xiantao City (population 1.2 million) to the east. Therefore, comprehensive monitoring is needed to address Both cities are located in the mid-downstream region of changes in water quality in this area. Accordingly, the ob- Hanjiang River. The area belongs to the subtropical monsoon jectives of this study are to apply and evaluate the use of climate zone, with mild climate characterized by four distinct Downloaded by University of Connecticut e-journal package NERL from online.liebertpub.com at 07/05/17. For personal use only. FIG. 1. Mosaic map made with Landsat 8 image (Red: 630–680 nm, Green: 525–600 nm, Blue: 450–515 nm) collected on June 13, 2013, showing the study area and location of Hanjiang River in China. Yellow points represent the data of 15 samples for modeling of each image. Yellow cross represents the data of 5 samples for validation of each image. RIVERINE TURBIDITY MONITORING BY LANDSAT 8 3 Table 1. Description of In Situ Turbidity Within Study Area Sampling Turbidity Mean Standard Sampling date number Sampling time range (NTU) value (NTU) deviation (NTU) April 26, 2013 20 02:46UTC–05:39UTC 20.8–49.7 32.3 7.10 June 13, 2013 20 01:52UTC–05:06UTC 39.3–54.4 47.5 4.66 November 20, 2013 20 02:44UTC–06:04UTC 15.8–25.9 20.3 2.62 January 23, 2014 20 01:45UTC–04:56UTC 47.2–130.2 75.5 29.15 NTU, nephelometric turbidity units. seasons, abundant rainfall, a long (256 days) frost-free pe- at 30-m spatial resolution, and one panchromatic channel at riod, 2002.6 annual average sunshine hours, and an average 15-m spatial resolution. Five good-quality Level 1T OLI annual temperature of 16.3°C. The division into seasons is images were obtained from the U.S. Geological Survey based on an average temperature below 10°C during winter, a (USGS) website (http://earthexplorer.usgs gov). The images temperature above 22°C during summer, and temperatures covering the area downstream of the Hanjiang River were between 10°C and 22°C during spring and autumn. Spring examined in detail (Table 2). With reference to some pub- lasts from roughly mid-March to mid-May (about 70 days), lished literatures (Shi et al., 2015; Zhang et al., 2016b), tur- summer from late May to mid-September (about 120 days), bidity was investigated using OLI band 1 (433–453 nm, autumn from late September to mid-November (about which was not featured on previous Landsat satellites), band 65 days), and winter from late November to early March 2 (450–515 nm), band 3 (525–600 nm), band 4 (630–680 nm), (about 110 days). In the study area, the southern part of the and band 5 (845–885 nm). Hanjiang River is characterized by industrial installations, including auto part, pharmaceutical, chemical, electronic, and nonwoven fabric factories, while the northern part of the Data preprocessing of OLI imagery river is mainly characterized by aquaculture and farming. Standard Landsat 8 OLI images consist of quantized, ca- librated, and scaled digital numbers (DNs) representing Field survey data multispectral image data, which are delivered in 16-bit un- Four field surveys were conducted in the study area be- signed integer format.