Sergio Florêncio de Souza

Regional Mapping of the Geoid Using GNSS (GPS) Measurements and an Artificial Neural Network

The determination of the orthometric height from geometric leveling has practical difficulties that, despite a number of scientific and technological advances, passed a century without substantial modifications or advances. Currently, the Global Navigation Satellite System (GNSS) has been used with reasonable success for orthometric height determination. With a sufficient number of benchmarks with known horizontal and vertical coordinates, it is often possible to adjust using the least squares method mathematical expressions that allow interpolation of geoid heights. The objective of this study is to present an alternative method to interpolate geoid heights based on the technique of Artificial Neural Networks (ANNs). The study area is the Brazilian state of Sao Paulo, and for training the ANN the authors have used geoid height information from the EGM08 gravity model with a grid spacing of 10 minutes of arc. The efficiency of the model was tested at 157 points with known geoid heights distributed across the study area. The results were also compared with the Brazilian Geoid Model (MAPGEO2004). Based on those 157 benchmarks it was possible to verify that the model generated by ANNs provided a mean absolute error of 0.24 m in obtaining a geoid height value. Statistical tests have shown that there was no difference between the means from known geoid heights and geoid heights provided by the neural model for a significance level of 5%. It was also found that ANNs provided an improvement of 2.7 times in geoid height estimates when compared with the MAPGEO2004 geoid model.

Recent trends in annual snowline variations in the northern wet outer tropics: case studies from southern Cordillera Blanca, Peru

This paper describes the changes in the annual maximum snowlines of a selected set of mountain glaciers at the southern end of the Cordillera Blanca between 1984 and 2015 using satellite images. Furthermore, we analysed the existing glacier records in the Cordillera Blanca since the last glacial maximum to understand the evolution of glaciers in this region over a few centuries. There was a rise in the snowline altitude of glaciers in this region since the late 1990s with a few small glacier advances. Historical to the present El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) records were also analysed to understand whether there was a teleconnection between the glacier fluctuations in the region and the phase changes of ENSO and PDO. We also assessed the variations in three important climatic parameters that influence the glacier retreat—temperature, precipitation, and relative humidity—over a few decades. We calculated the anomalies as well as the seasonal changes in these variables since the mid-twentieth century. There was an increase in temperature during this period, and the decrease in precipitation was not so prominent compared with the temperature rise. There was an exceptionally higher increase in relative humidity since the early 2000s, which is relatively higher than that expected due to the observed rate of warming, and this increase in humidity is believed to be the reason behind the unprecedented rise in the snowline altitudes since the beginning of the twenty-first century.

Variations in annual snowline and area of an ice-covered stratovolcano in the Cordillera Ampato, Peru, using remote sensing data (1986–2014)

This research focuses on the recent variations in the annual snowline and the total glaciated area of the Nevado Coropuna in the Cordillera Ampato, Peru. Maximum snowline altitude towards the end of dry season is taken as a representative of the equilibrium line altitude of the year, which is an indirect measurement of the annual mass balance. We used Landsat and IRS LISS3 images during the last 30 years due to its better temporal coverage of the study site. It is found that there was a decrease of 26.92% of the glaciated area during 1986–2014. We calculated the anomalies in precipitation and temperature in this region and also tried to correlate the changes in glacier parameters with the combined influence of El Niño – Southern Oscillation (ENSO) and pacific decadal oscillation (PDO). It is concluded that the snowline of Nevado Coropuna has been fluctuated during ENSO, and maximum fluctuations were observed when ENSO and PDO were in phase.

Recent Changes Occurred in the Terminus of the Debris- covered Bilafond Glacier in the Karakoram Himalayas Using Remotely Sensed Images and Digital Elevation Models (1978-2011)

Recent changes occurred in terminus of the debris-covered Bilafond Glacier in the Karakoram Range in the Himalayas, Northern Pakistan was investigated in this research. Landsat MSS, TM and ETM+ images were used for this study. Digital elevation models derived from ASTER GDEM and SRTM were also utilized. Visible, infrared and thermal infrared channels were utilized in order to get accurate glacier change maps. Three methods were tried to map this debris-covered glacier in this research. The glacier has been mapped successfully and the changes in the glacier terminus from 1978 to 2011 have been calculated. Manual, semi-automatic and thermal methods were found to give similar results. It was found that the glacier has undergone serious ablation during this period despite of the fact that many of the larger glaciers in the Hindu Kush and Karakoram mountain regions in the Upper Indus Basin were reported to be expanding. The terminus has been moved back about 600 meters during this period and there was an abrupt change in the glacier terminus during 1990–2002. We propose that debris thickness is not the only factor that influences the glacier ablation but the altitude of the debris-covered glacier as well. Many glaciers in the Karakoram region reported to be expanding were having higher altitudes compared to the study area.

Decadal evolution of glaciers and glacial lakes in the Apolobamba–Carabaya region, tropical Andes (Bolivia–Peru)

ABSTRACT This paper presents the first decadal quantification of glacier area in the cordilleras Carabaya and Apolobamba in Peru and Bolivia (14°00′–14°39′S; 69°14′–70°19′W). We calculated the changes in glacier area between 1975 and 2015 and the number of glacial lakes between 1985 and 2015 using Landsat images. Glacier shrinkage in our study region was most likely to have caused the expansion of numerous glacial lakes in recent decades. In contrast to observed glacier fluctuations in the western cordilleras of the tropical Andes, continuous glacier shrinkage was observed in the eastern cordilleras of Peru and Bolivia. The estimated glacier mean area loss between 1975 and 2015 in the Cordillera Apolobamba and the Cordillera Carabaya was about 51% and 79%, respectively. Glaciers situated below 5000 m a.s.l. nearly disappeared (93% and 95.5% in the cordilleras Apolobamba and Carabaya, respectively) during this period, but glaciers above 5500 m a.s.l. were relatively stable (13.5% and 31% in Apolobamba and Carabaya, respectively). Further on, glacier area loss by aspect revealed that glaciers oriented towards the Amazon Basin were retreating faster (74.5% and 86%, respectively) than those oriented towards the Pacific coast (40% and 68%, respectively). We observed the formation of 206 new glacial lakes between 1985 and 2015 in these two mountain ranges with an increase in the total area of 3.8 km2, which is a significant growth in just 30 yr.

Influence of ENSO and PDO on mountain glaciers in the outer tropics: case studies in Bolivia

This paper emphasize on the observational investigation of an ice-covered volcano and two glaciated mountains in the Central Andes from 1984 to 2011. Annual snowlines of the Nevado Sajama in the Cordillera Occidental and the Nevado Cololo and the Nevado Huanacuni in the Cordillera Apolobamba in Bolivia were calculated using remote sensing data. Landsat TM, Landsat ETM+, and LISS-III images taken during the end of dry season were used in this study. Changes in the highest annual snowline during May–September is used an indirect measure of the changes in the equilibrium line altitude of the glaciers in the outer tropics. We tried to understand the combined influence of the El Niño-Southern Oscillation and the Pacific Decadal Oscillation on the variations in the annual snowline altitude of the selected glaciers. Meteorological data in the form of gridded datasets were used for calculating the anomalies in precipitation and temperature during the study period. It is found that the glaciated areas were fluctuated with the occurrence of warm and cold phase of ENSO but the magnitude of the influence of ENSO is observed to be controlled by the phase changes of PDO. Snowline of the Nevado Sajama fluctuated heavily when cold and warm phases of ENSO occur during the cold and warm regimes of PDO, respectively. Nevado Cololo and Nevado Huanacuni are showing a continuous retreating trend during the same period. This clearly indicates that the changes in the Pacific SST patterns have more influence on glaciers in the Cordillera Occidental compared with those in the Cordillera Oriental of the Bolivian Andes.

Study of 40-year glacier retreat in the northern region of the Cordillera Vilcanota, Peru, using satellite images: preliminary results

ABSTRACT In this article, the possibility of using a Landsat image series to calculate the decadal changes in the area of mountain glaciers in the eastern cordillera of Peru is explored. In the pilot study site, changes in the glacier area at different elevation ranges to understand the altitudinal gradients and the directional properties of glacier retreat during the period 1975–2015 were calculated. This approach can be used in the entire tropical Andes, particularly in the outer tropics, depending on the availability of cloud-free images during the dry season. Similar to other regions in the tropical Andes, glaciers situated below 5000 m a.s.l. have lost nearly 81% of the initial area. It is observed that those glaciers directed towards north-east and east shows higher retreat and this may influence the glacier-fed rivers in the Amazon Basin. Future research will estimate the glacier variations in the entire eastern cordilleras and the corresponding changes in the water discharge volume in the Amazon Basin.

Planejamento de redes geodésicas resistentes a múltiplos outliers

Ao se planejar o levantamento de uma rede geodesica, deseja-se que as observacoes a serem realizadas e as coordenadas dos pontos a serem estimadas atendam criterios de precisao e confiabilidade pre-estabelecidos de acordo com os objetivos do projeto. Na etapa de pre-analise, antes mesmo da coleta das observacoes, e possivel estimar a precisao e confiabilidade da rede, estipulando uma geometria/configuracao para a mesma e a precisao esperada para as observacoes. O objetivo deste artigo e apresentar o planejamento de uma rede geodesica que atenda criterios de precisao e confiabilidade, considerando a possivel existencia de dois ou mais erros nao detectados nas observacoes, bem como a influencia (simultânea) destes erros sobre os parâmetros (coordenadas ajustadas dos vertices). Alem da revisao teorica, experimentos foram realizados em uma rede GNSS, onde foram estipulados criterios de precisao e confiabilidade considerando a existencia de ate duas observacoes contaminadas por erros (outliers), de maneira simultânea. O planejamento da rede foi feito por meio do metodo da tentativa e erro. Depois do processamento dos dados e do ajustamento da rede, se verificou que os criterios de precisao e confiabilidade que foram estipulados na etapa de pre-analise foram devidamente obtidos.

Un análisis comparativo del comportamiento diferencial de los glaciares en los Andes Tropicales usando teledetección

En este trabajo de investigacion, se analizo el comportamiento de los glaciares de los Andes Tropicales en un clima cambiante; para esto se emplearon imagenes satelitales multiespectrales de diversas fuentes en conjunto con datos meteorologicos. El estudio se enfoco en glaciares representativos de cuatro zonas climaticas diferentes, a saber: tropicos interiores, tropicos exteriores humedos del norte, tropicos exteriores humedos del sur y tropicos exteriores secos. Se calcularon los cambios en la linea de nieve maxima anual para el periodo de 1985―2015, y tambien los cambios decenales en el area entre 1975 y 2015. Ademas, se analizo la tasa de retroceso de los glaciares durante la ocurrencia de El Nino―Oscilacion del Sur y la Oscilacion Decenal del Pacifico. Se observo que los glaciares tanto de los tropicos interiores como de los tropicos exteriores se sometieron a retroceso durante todo el periodo de estudio, con enfasis entre 1975 y 1997, lapso coincidente con el periodo de calentamiento del Pacifico. Se observaron variaciones excepcionales en la altitud de la linea de nieve cuando se produce un evento de El Nino durante la fase calida de la Oscilacion Decenal del Pacifico. Se observo que no hay senales significativas del hiato reciente en el calentamiento global, excepto en los tropicos exteriores secos, localizados cerca de la region subtropical.

DTM generation from a stereo pair acquired by the China-Brazilian Earth Resources Satellite (CBERS-2) and quality control of the altimetric information

The CBERS (China–Brazilian Earth Resources Satellite) program comprised a bilateral collaboration between Brazil and China for the development, construction and launch of at least two remote sensing satellites on a sun-synchronous, 778 km orbit, carrying onboard three imaging systems (High Resolution Charge Coupled Device (HR-CCD) Camera; infrared multispectral scanner IRMSS and wide field imager (WFI)). CBERS-1 and CBERS-2 were launched in October 1999 and October 2003, respectively, and acquired data using a similar technical structure, space mission and payload. The CCD camera provides images with 113 km swath, 20 m spatial resolution and has a sideways pointing capability of ±32˚, which makes possible the acquisition of stereoscopic images. This research focused on the extraction of altimetric information from a stereo pair acquired by the CBERS-2’s HR-CCD Camera, using digital photogrammetry techniques. Additionally, a quantitative precision and accuracy analysis of the altimetric information was carried out. Tests showed a root mean square error (RMSE) value of 38 m in the computed digital terrain model (DTM) against test points extracted from existing elevation data. The correction of such bias decreased the RMSE to 27 m. Considering Brazilian Cartographic Accuracy Standards (BCAS), this altimetric information can be used for Class A cartographic documents at scales up to 1:250 000.