Network Of Control Points Research Articles

Phobos control point network, rotation, and shape

A new independent control point network for Phobos was computed from image data obtained by the SRC (Super Resolution Channel) on board the European Mars Express Mission. The network solution includes 3D coordinates of 665 surface control points and was used to observe the forced libration amplitude of Phobos. Based on the network control points a spherical harmonic function model to degree and order 17 was derived, from which volume, bulk density and moments of inertia were computed. The modeled forced libration amplitude agrees to our observation within the error bands, indicating a homogeneous mass distribution for Phobos. To bring both values into exact agreement with the observations, different mass distribution models were applied. It appears that the amplitude is relatively insensitive to a simple two-layer density model.

Assessing the geometric accuracy of AVHRR data processed with a state vector based navigation system

We evaluate the geometric accuracy of Advanced Very High Resolution Radiometer (AVHRR) data processed using the Common AVHRR Processing System (CAPS) software. Accurate geometric correction, to known standards, of satellite images is crucial for many remote sensing applications, especially those using a time series of images and integrating other spatially referenced datasets. It is critical that data acquired by satellites with short repeat intervals (e.g., daily) are geolocated using methods that are both automatic and reliable. Landsat Enhanced Thematic Mapper Plus (ETM+) high-resolution imagery was used to establish ground control point (GCP) networks for two coastal regions of Australia, one tropical with 40 GCPs and one temperate with 60 GCPs. The geolocation accuracy was assessed for a total of 12 and 13 AVHRR images, respectively, against the GCPs for each region, respectively, totalling 1039 cloud-free GCP comparisons. Results showed that when the view zenith angle was less than 40°, the average (±1 standard deviation) accuracies are 0.36 ± 0.31 and 0.44 ± 0.35 of an at-nadir AVHRR pixel (1.1 km × 1.1 km) in the cross-track direction for the tropical and temperate regions, respectively, and 0.30 ± 0.26 and 0.36 ± 0.29 at-nadir AVHRR pixel in the along-track direction for the tropical and temperate regions, respectively. For higher satellite view zenith angles, the geometric accuracy decreases systematically with an increase in the pixel size towards the edges of the AVHRR swath.

Using of GPS and Leveling Techniques for Determining the Orthometric Heights inside Mosul University

It is possible to determine heights of selective locations through terrestrial means by tying these locations to the sea level. Practical heights in geodesy, known as orthometric heights are referred to the geoid, which is approximated by the mean sea level (MSL). In the present study, A GPS and conventional leveling techniques were used to establish a network of (15) control points distributed inside Mosul University Campus, to be as a bench marks for the surveying applications which are very important and necessary for the civil engineering projects and the geophysical survey. The obtained results show that, there is an average variation between the orthometric heights measured by leveling instrument and the ellipsoidal heights measured by GPS, referred to as geoid undulation. ArcGIS9.1 software was applied in the study for the georeferencing process of the GPS measured dataset. Keywords: GPS, orthometric height, mean sea level

A method to test differences between additional parameter sets with a case study in terrestrial laser scanner self-calibration stability analysis

This paper presents a new method for quantitatively assessing the impact and therefore the significance of differences between sets of additional parameters used to model systematic sensor errors. Focusing on bundle reconstruction at the sensor, simulation-based techniques have recently been proposed as superior methods to standard parameter-space hypothesis testing. This paper experimentally demonstrates the shortcoming of this approach and proposes an improved method that tests the effect of additional parameter differences on object reconstruction, which is generally of primary interest in photogrammetry. Additionally, the arbitrariness in selecting only one or two object space configurations is overcome with the new method by simulating a large number of randomly-generated but realistic control point networks for sensor orientation and a dense grid of points for object reconstruction. The experimental subject of the paper is a Faro 880 terrestrial laser scanner for which 10 sets of calibration parameters have been captured over a 13-month period. While standard parameter-space hypothesis testing indicates the instrument is not stable over this time, the new procedure shows that this is not true in all instances.

Mapping forest plots: an efficient method combining photogrammetry and field triangulation

Intra stand spatial information is often collected in ecological investigations, when functioning or interactions in the ecosystem are studied. Local relative accuracy is often given priority in such cases. Forest maps with accurate absolute positions in a global coordinate system are needed in remote-sensing applications for validation and calibration purposes. Establishing the absolute position is particularly difficult under a canopy as is creating undistorted coordinate systems for large plots in the forest. We present a method that can be used for the absolute mapping of point features under a canopy that is efficient for large forest plots. In this method, an undistorted network of control points is established in the forest using photogrammetric observations of treetops. These points are used for the positioning of other points, using redundant observations of interpoint distances and azimuths and a least squares adjustment. The method provides decimetre-level accuracy and only one person is required to conduct the work. An estimate of the positioning accuracy of each point is readily available in the field. We present the method, a simulation study that explores the potential of the method and results from an experiment in a mixed boreal stand in southern Finland.

Can old analogue sidescan sonar data still be useful? An example of a sonograph mosaic geo-coded by the DECCA navigation system

In the Baltic and the North Sea area the collection of sidescan sonar data began in the early 1970s. Although positioning systems at that time were much less accurate than today, such analogue data archives are a valuable source of comparison for estimating spatial and temporal changes in sediment patterns. This paper describes how geographic information systems (GIS) and remote sensing methods are being applied for more accurate positioning and geometric correction of analogue sidescan sonar profiles geo-referenced by the DECCA navigation system (DNS). A 20 km 2 area in the North Sea, where even after 25 years a complicated sediment pattern has only changed slightly, was selected for the comparison. Data from two sidescan sonar surveys, one from 1977 and the other from 2002, were available. The 2002 data, acquired with a positioning accuracy of estimated 25 m, were mosaicked using modern digital processing techniques. This dataset was used to estimate positioning errors in the analogue sidescan sonar profiles of 1977. After the application of a geo-referencing method of ‘rubber sheeting’ based on an irregular network of ground control points to generate a mosaic of the analogue profiles, positioning errors of 211 m in the E–W and 98 m in the N–S directions were obtained. The positioning error of the DNS calculated from equations provided by the DECCAN Navigator Company for this area, was as large as 200 m for the ‘purple’ station transmission, 197 m for the ‘green’, and 66 m for the ‘red’ one. Consequently, we conclude that the observed positioning errors were mainly caused by systematic deviations of the DNS rather than simplifications used in our methodology. Since such large errors can be corrected locally with some confidence, analogue sidescan profiles geo-referenced by DNS can be used as a significant source of information after digital image processing at appropriate map scales.

Vertical control point network and global shape of Io

We have analyzed Galileo and Voyager images of Io to derive global control point networks, involving 402 (Galileo) and 158 (Voyager) surface points as well as combinations of the two data sets. Using block adjustment techniques, three‐dimensional coordinates of the control points are derived with an accuracy of 4.7 km (Galileo) and 8.6 km (Voyager). Three‐axial ellipsoids are fitted to the Galileo control points, for which we find the following: a = 1831.1 ± 0.3 km, b = 1820.4 ± 0.4 km, and c = 1816.6 ± 0.5 km. Our results on size and shape confirm that Io (in synchronous rotation and exposed to strong tidal and rotational forces) is in hydrostatic equilibrium and has a pronounced mass concentration toward the center, in agreement with suggested Fe‐ and Fe/S cores of 740 and 1000 km radius, respectively. However, our shape model is unable to resolve long‐wavelength topography beyond the ellipsoidal parameters. Studies of synthetic Galileo and Voyager control point data sets are carried out to track error propagation in our control point networks and to compare the geometric performance of the two spacecraft cameras. We find that Voyager Vidicon images suffer from residual geometric errors on the order of 1/3 of a pixel, which adds to the typical image coordinate measurement errors (slightly less than 1/2 pixel) that apply for Galileo or Voyager images alike. We therefore suggest that previous authors have overestimated the accuracy of their Voyager‐based control point networks and global topographic maps significantly.

Achieving sub-pixel geolocation accuracy in support of MODIS land science

The Moderate Resolution Imaging Spectroradiometer (MODIS) was launched in December 1999 on the polar orbiting Terra spacecraft and since February 2000 has been acquiring daily global data in 36 spectral bands—29 with 1 km, five with 500 m, and two with 250 m nadir pixel dimensions. The Terra satellite has on-board exterior orientation (position and attitude) measurement systems designed to enable geolocation of MODIS data to approximately 150 m (1 σ) at nadir. A global network of ground control points is being used to determine biases and trends in the sensor orientation. Biases have been removed by updating models of the spacecraft and instrument orientation in the MODIS geolocation software several times since launch and have improved the MODIS geolocation to approximately 50 m (1 σ) at nadir. This paper overviews the geolocation approach, summarizes the first year of geolocation analysis, and overviews future work. The approach allows an operational characterization of the MODIS geolocation errors and enables individual MODIS observations to be geolocated to the sub-pixel accuracies required for terrestrial global change applications.

The Mars NetLander panoramic camera

The panoramic camera (PanCam) imaging experiment is designed to obtain high-resolution multispectral stereoscopic panoramic images from each of the four Mars NetLander 2005 sites. The main scientific objectives to be addressed by the PanCam experiment are (1) to locate the landing sites and support the NetLander network sciences, (2) to geologically investigate and map the landing sites, and (3) to study the properties of the atmosphere and of variable phenomena. To place in situ measurements at a landing site into a proper regional context, it is necessary to determine the lander orientation on ground and to exactly locate the position of the landing site with respect to the available cartographic database. This is not possible by tracking alone due to the lack of on-ground orientation and the so-called map-tie problem. Images as provided by the PanCam allow to determine accurate tilt and north directions for each lander and to identify the lander locations based on landmarks, which can also be recognized in appropriate orbiter imagery. With this information, it will be further possible to improve the Mars-wide geodetic control point network and the resulting geometric precision of global map products. The major geoscientific objectives of the PanCam lander images are the recognition of surface features like ripples, ridges and troughs, and the identification and characterization of different rock and surface units based on their morphology, distribution, spectral characteristics, and physical properties. The analysis of the PanCam imagery will finally result in the generation of precise map products for each of the landing sites. So far comparative geologic studies of the Martian surface are restricted to the timely separated Mars Pathfinder and the two Viking Lander Missions. Further lander missions are in preparation (Beagle-2, Mars Surveyor 03). NetLander provides the unique opportunity to nearly double the number of accessible landing site data by providing simultaneous and long-term observations at four different surface locations which becomes especially important for studies of variable surface features as well as properties and phenomena of the atmosphere. Major changes on the surface that can be detected by PanCam are caused by eolian activities and condensation processes, which directly reflect variations in the prevailing near-surface wind regime and the diurnal and seasonal volatile and dust cycles. Atmospheric studies will concentrate on the detection of clouds, measurements of the aerosol contents and the water vapor absorption at 936 nm. In order to meet these objectives, the proposed PanCam instrument is a highly miniaturized, dedicated stereo and multispectral imaging device. The camera consists of two identical camera cubes, which are arranged in a common housing at a fixed stereo base length of 11 cm. Each camera cube is equipped with a CCD frame transfer detector with 1024×1024 active pixels and optics with a focal length of 13 mm yielding a field-of-view of 53°×53° and an instantaneous filed of view of 1.1 mrad. A filter swivel with six positions provides different color band passes in the wavelength range of 400–950 nm. The camera head is mounted on top of a deployable scissors boom and can be rotated by 360° to obtain a full panorama, which is already covered by eight images. The boom raises the camera head to a final altitude of 90 cm above the surface. Most camera activities will take place within the first week and the first month of the mission. During the remainder of the mission, the camera will operate with a reduced data rate to monitor time-dependent variations on a daily basis. PanCam is a joint German/French project with contributions from DLR, Institute of Space Sensor Technology and Planetary Exploration, Berlin, Institut d'Astrophysique Spatiale, CNRS, Orsay, and Service d'Aéronomie, CNRS, Verrières-le-Buisson.

The shape of Mars before Global Surveyor: Results from reanalysis of the Viking control point network

Three‐dimensional coordinates of 3739 globally distributed control points derived from photogrammetric analysis of Viking Orbiter image data are studied with respect to the shape and large‐scale morphology of Mars. Spheres, spheroids, spherical functions, and a Digital Terrain Model (DTM) of 50 km grid spacing are fitted to the data. Prominent topographic features in the terrain model include the Tharsis volcanoes, Olympus Mons, Alba Patera and prominent mare and highland regions as well as the major impact basins. While the global dichotomy is clearly visible in our data, our model does not reveal any distinct signature associated with the presumed dichotomy boundary at this global scale. Rather, it suggests a smooth topographic transition from southern to northern hemisphere. This model is unique among existing topographic data sets for Mars, as it combines global coverage, a spatial resolution sufficient to resolve regional topography, and absolute elevation data more accurate than in previous control point network analyses. Formal errors and a comparison with the first released topographic profiles obtained by Mars Global Surveyor's Laser Altimeter (MOLA) suggest that 70% and 90% of the DTM grid elements represent the topography of the planet to better than 1000 m and 2000 m, respectively.

The Mars Pathfinder landing site and the Viking control point network

We recomputed the Viking Mars control point network and derived Mars‐fixed three‐dimensional coordinates of 3739 selected, globally distributed landmarks. Mars Pathfinder and Viking Lander 1 coordinates as well as data from reanalyzed spacecraft occultation measurements are used as fixed control information in the analysis. The network benefits greatly from recently restored Viking orbiter trajectory data and new planet rotational parameters derived from Pathfinder lander tracking. In our attempt to predict the coordinates of the Viking Lander 1 site from given Pathfinder coordinates, we find an offset of ≈4–5 km of this lander location with respect to the previously reported data. We suggest that this probably is explained by erroneous identification of this landing site in the images. Ninety percent of our landmark coordinates have positional errors of less than 1800 m. This network thus removes previously noted severe offsets between Mars‐fixed coordinates and cartographic products.

Photogrammetric analysis of horizon panoramas: The Pathfinder landing site in Viking orbiter images

Tiepoint measurements, block adjustment techniques, and sunrise/sunset pictures were used to obtain precise pointing data with respect to north for a set of 33 IMP horizon images. Azimuth angles for five prominent topographic features seen at the horizon were measured and correlated with locations of these features in Viking orbiter images. Based on this analysis, the Pathfinder line/sample coordinates in two raw Viking images were determined with approximate errors of 1 pixel, or 40 m. Identification of the Pathfinder location in orbit imagery yields geological context for surface studies of the landing site. Furthermore, the precise determination of coordinates in images together with the known planet‐fixed coordinates of the lander make the Pathfinder landing site the most important anchor point in current control point networks of Mars.

Performance Evaluation of Automated Vehicle Locator and Digital Map Accuracy in Transit Application

New Jersey Transit (NJT) is investigating acquisition of an automated vehicle locator (AVL) system. The purpose of the AVL system is to monitor the location of buses. Knowing the location of a bus allows the operator to manage the bus fleet more efficiently and to provide customers with up-to-the-minute information on bus arrivals and departures. To monitor the location of the buses, their positional information (as determined by the AVL) is displayed on a digital map such as a geographic information system. To ensure accurate information, the location (coordinates) of the bus must be consistent (or within a small tolerance) with those of the digital map. If this is not the case, the system can yield incorrect information. This problem might become especially critical in an urban area where the system would be most valuable. The methodology that was developed for testing and evaluating the accuracies of AVL systems and available digital maps is described. The AVL system analyzed is the continuous positioning system by Andrew Corporation. Digital mapping products evaluated were TIGER, Navtech, and Digital Orthophotos. These data sets were evaluated with an accurate network of control points measured by a global positioning system. Some recommendations on the appropriateness of the tested AVL system and NJT’s digital mapping data are made.

Radiometric standardization of multispectral satellite data over mountainous terrain

A method to correct atmospheric effects on Landsat‐TM data over mountainous terrain in the solar spectrum was developed primarily for forestry applications, but can also be adapted to other sensors and applications. The algorithm automatically identifies patches of dark, dense vegetation as controllable dark surfaces for the purpose of estimating aerosol optical thickness. Thereby a network of radiometric control points, rendering both horizontal as well as relief induced vertical changes of atmospheric conditions, is expanded over a scene. Atmospheric parameters calculated with LOWTRAN over these pixels are smoothed and interpolated by cubic spline regression. With these values atmospherically corrected ground reflectances are calculated pixelwise by iteration of a correction model. Improvements in visual interpretation, in the standardization of photo products and in the use of calibrated data with multitemporal applications are discussed.

Low altitude, small format aerial photogrammetry

Abstract This project describes the use of 35 mm format non-metric photography for estimating earth work. The aerial pictures were taken from 35 mm super high speed, non-metric cameras mounted on remote-controlled model aeroplane. Results from a test-bed using a network of ground control points suggest that the accuracy of obtaining X, Y, Z ground co-ordinates from digitized enlarged positive prints using desk-top digitizers was adequate for most engineering work.

Conventional terrestrial system by VLBI a kinematic approach

The paper examines the potential ofVLBI time delay observables for the establishment and maintenance of a Conventional Terrestrial System (CTS). TheCTS is defined in2-D by the standard epoch positions and velocities of a network of control points located on a spherical reference surface.

Conventional Terrestrial System by VLBI: A Kinematic Approach

The paper examines the potentials of VLBI time delay observables for the establishment and maintenance of a Conventional Terrestrial System (CTS). The CTS is defined in 2-D by the standard epoch positions and velocities of a network of control points located on a spherical reference surface.

The impact of VLBI and GPS on geodesy

Two new technologies, Very Long Baseline Interferometry (VLBI) and the Global Positioning System (GPS), will provide the means for achieving the perennial goal of geodesists—a unified, worldwide geodetic control point network tied to an inertial reference system. VLBI will replace optical methods for determining both polar motion and rotation rate, with accuracies an order of magnitude better and with results available a week or less after observations. GPS will permit rapid, economical point positioning with accuracies of a few centimeters over distances of 100 km or more. The potential of these new systems will generate new applications for geodesy and require a reevaluation of the role of geodesists

A history of Mars atmospheric opacity in the Southern Hemisphere during the Viking extended mission

A history of developing opacity in the Mars southern hemisphere during the Viking extended mission has been compiled using orbiter images obtained at high altitude. Observations of changing contrasts under similar viewing conditions have been modeled by multiple‐scattering intensity transfer equations that have produced a temporal description of changes in optical depth and particle‐scattering properties within a network of control points. The results are presented in the form of Mercator and perspective plots for various dates.

Herstellung von Luftbildkarten in der Provinz Ta'izz (Arabische Republik Jemen)

Abstract. This article deals with a simple method to produce photomaps of as yet unsurveyed areas. Since a triangulation network or a topographic inventory of the areas to be mapped did not exist, it was considered most suitable to produce some kind of «preliminary maps»: Maps of medium accuracy but high content of information which could be produced within a short time with modest technical means and at low cost. The following procedure was found to be most suitable for that purpose. A network of control points is established by means of the slotted templet method. Aerial photographs,dodged by the Log Etronic procedure, are assembled to semicontrolled mosaics. Grestlines, plateau edges and Symbols for mountain peaks, passes etc. as well as spot heights, roads, tracks, wells, market places and names of Settlements, districts and surface features are introduced into the photomosaics by means of transparent overlays. This latter Information was collected during a three months' field survey in the Yemen Arab Republic.