Delineating agricultural field boundaries from TM imagery using dyadic wavelet transforms

Agricultural field boundary information is important in the study of agricultural crops by remote sensing. In this paper, the dyadic wavelet transform is adopted to extract field boundaries directly from TM imagery. A field boundary is a set of locally connected pixels characterized by their abrupt spectral intensity variation (singularity) on the image. Preliminary extraction is made on the near-infrared Band 4 (0.76–0.90 μm) image. It is found that most of the boundaries are well characterized by the wavelet modulus maxima curves, particularly for fully vegetated fields, while better results are obtained from the NDVI image for cropped field boundaries. To extract additional boundaries while suppressing unwanted noisy edges, the wavelet transform is then applied to the Wetness image calculated by the Tasselled Cap Transform. A technique is implemented to integrate the edges extracted from each source. The combined results show that the majority of the field boundaries are delineated. The use of a single date image fails to delineate some of the fallow field boundaries and boundaries between two cropped fields with similar spectral properties. Although techniques have been applied to reduce noise, still great difficulties are encountered when trying to delineate edges that are field boundaries from all the detected singularities. Manual editing is still required to trace the remaining boundaries to obtain a complete boundary map. It is recommended that a multi-temporal data set be used to obtain a complete delineation with a fully automated algorithm.     

Response of GPS occultation signals to atmospheric gravity waves and retrieval of gravity wave parameters

We show that the amplitude of the Global Positioning System (GPS) signals in the radio occultation (RO) experiments is an indicator of the activity of the gravity waves (GW) in the atmosphere. The amplitude of the GPS RO signals is more sensitive to the atmospheric wave structures than is the phase. Early investigations used only the phase of the GPS occultation signals for statistical investigation of the GW activity in the height interval 10–40 km on a global scale. In this study, we use the polarization equations and Hilbert transform to find the 1-D GW radio image in the atmosphere by analyzing the amplitude of the RO signal. The radio image, also called the GW portrait, consists of the phase and amplitude of the GW as functions of height. We demonstrate the potential of this method using the amplitude data from GPS/Meteorology (GPS/MET) and satellite mission Challenge Mini-satellite Payload (CHAMP) RO events. The GW activity is nonuniformly distributed with the main contribution associated with the tropopause and the secondary maximums related to the GW breaking regions. Using our method we find the vertical profiles of the horizontal wind perturbations and its vertical gradient associated with the GW influence. The estimated values of the horizontal wind perturbations are in fairly good agreement with radiosonde data. The horizontal wind perturbations v(h) are ±1 to ±5 m s with vertical gradients dv/dh ±0.5 to ±15 m s km at height 10–40 km. The height dependence of the GW vertical wavelength was inferred through the differentiation of the GW phase. Analysis of this dependence using the dispersion relationship for the GW gives the estimation of the projection of the horizontal background wind velocity on the direction of the GW propagation. For the event considered, the magnitude of this projection changes between 1.5 and 10 m s at heights of 10–40 km. We conclude that the amplitude of the GPS occultation signals contain important information about the wave processes in the atmosphere on a global scale.     

Urban change detection related to earthquakes using an adaptive nonlinear mapping of high-resolution images

We propose a nonlinear mapping method for detecting geographical changes. In our system, two images photographed at different points of time are checked based on an iterative nonlinear mapping. The system automatically extracts feature changes of aerial imageries by computing distribution of the image matching score. We evaluate the change detection ability by using the receiver operating characteristic under misregistration cases, including rotational misalignments.     

Evaluation of Information Loss in Digital Elevation Models With Digital Photogrammetric Systems

Information loss is caused when a surface is sampled with a finite interval, such as in the production of a digital elevation model (DEM). This information loss can become the dominant part of the error in a DEM. The ability to quantify information loss enables guidance to be provided for an appropriate choice of grid interval and better accuracy assessment for the DEM. With the use of digital photogrammetric systems, evaluation of information loss has become much easier. This paper describes three methods of evaluating information loss. An example is given of the method which is most appropriate for use with a digital photogrammetric system, based on rock cliff surface data and the VirtuoZo system.     

Maximum-likelihood ambiguity resolution based on Bayesian principle

 Based on the Bayesian principle and the fact that GPS carrier-phase ambiguities are integers, the posterior distribution of the ambiguities and the position parameters is derived. This is then used to derive the maximum posterior likelihood solution of the ambiguities. The accuracy of the integer ambiguity solution and the position parameters is also studied according to the posterior distribution. It is found that the accuracy of the integer solution depends not only on the variance of the corresponding float ambiguity solution but also on its values. Received: 27 July 1999 / Accepted: 22 November 2000     

巴黎能力建设委员会助力全球气候治理

在全球气候治理中,能力建设涉及减缓、适应等多个方面.相对于发达国家,发展中国家在应对气候变化能力方面存在更多挑战,也亟待支持.巴黎能力建设委员会(PCCB)是《联合国气候变化框架公约》(以下简称公约)下属能力建设议题唯一的常设机构.在《巴黎协定》的授权下, PCCB于2016年成立,致力于解决发展中国家在实施和加强应对...     

Past,present and future vegetation-cloud feedbacks in the Amazon Basin

To begin exploring the underlying mechanisms that couple vegetation to cloud formation processes, we derive the lifting condensation level (LCL) to estimate cumulus cloud base height. Using a fully coupled land–ocean–atmosphere general circulation model (HadCM3LC), we investigate Amazonian forest feedbacks on cloud formation over three geological periods; modern-day (a.d. 1970–1990), the last glacial maximum (LGM; 21 kya), and under a future climate scenario (IS92a; a.d. 2070–2090). Results indicate that for both past and future climate scenarios, LCL is higher relative to modern-day. Statistical analyses indicate that the 800 m increase in LCL during the LGM is related primarily to the drier atmosphere promoted by lower tropical sea surface temperatures. In contrast, the predicted 1,000 m increase in LCL in the future scenario is the result of a large increase in surface temperature and reduced vegetation cover.     

Controlling factors of the δ 11B-pH proxy and its research direction

Significant boron isotope fractionation occurs in nature (?70 ‰ to +75 ‰) due to the high geochemical reactivity of boron and the large relative mass difference between ¹⁰B and ¹¹B. Since the 1990s, reconstruction of ancient seawater pH using the isotopic composition of boron in bio-carbonates (δ ¹¹B_carb), and then calculation of the past pCO₂ have become important issues for the international isotope geochemistry community, and are called the δ ¹¹B-pH proxy. Although many achievements have been made by this proxy, various aspects of boron systematics require rigorous evaluation. Based on the previous researches, mechanism of boron isotope fractionation, variation of boron isotope (δ ¹¹B) in nature (especially in bio-carbonates) and controlling factors of the δ ¹¹B-pH proxy, such as the dissociation constant of B(OH)₃ in seawater (pK_a), the δ ¹¹B of seawater (δ ¹¹B_SW), the boron isotopic fractionation factor between B(OH) ₄ ^? and B(OH)₃ (α _4–3), and the incorporated species of boron into bio-carbonates, are reviewed in detail and the research directions of this proxy are proposed. Generally, the controversy about pK_a, δ ¹¹B_sw, and α _4–3 is relatively less, but whether boron incorporated into bio-carbonates only in the form of B(OH) ₄ ^? remains doubtful. In the future, it is required that the physicochemical processes that control boron incorporation into carbonates be rigorously characterized and that the related chemical and isotopic fractionation be quantified. It is also necessary and important to establish a “best-fit empirically equation” between δ ¹¹B_carb and pH of seawater based on the precipitation experiments of inorganic or culture experiments of corals or foraminifera. In addition, extended application of the δ ¹¹B-pH proxy to the earlier part of the Phanerozoic relying on the Brachiopods is worthy of studying. Like other geochemical indicators, there are limiting factors of δ ¹¹B; however, it remains a very powerful tool in the reconstruction of past seawater pH at present.     

Coral recruitment onto an experimental pulverised fuel ash-concrete artificial reef

An experimental artificial reef was deployed in December 1993 at Hoi Ha Wan Marine Park, Hong Kong. This is the first study documenting natural scleractinian coral recruitment onto a stabilised pulverised fuel ash (PFA)-concrete artificial reef. Visible recruits were first recorded 9-10 months after the placement of reef blocks, i.e., in the autumn of 1994. Two scleractinians, Oulastrea crispata and Culicia japonica, were recruited. The recruit density of the former was much greater than the latter. The spatial recruitment pattern of the corals was observed to be affected by the orientation of the attaching surface. O. crispata settled predominantly on the undersides of the reef blocks. There was an edge effect on O. crispata recruitment. C. japonica, however, had a preference for exposed surfaces. O. crispata did not show a preference for block composition whereas C. japonica favoured blocks with high (75% by volume) PFA levels. This shows that PFA-concrete is a potential substratum for artificial reef construction, especially when such reefs aim at rehabilitating corals.