Abstract
As the important infrastructures for land mapping and resource monitoring, high-resolution remote sensing satellites (HRSS) are urgently demanded for the development of China. In this article, the key technologies of the main HRSS are summarized, and these technologies include sensor design, attitude and orbit determination, geometric calibration, imaging model construction, and block adjustment, etc., which involve the mapping accuracy of HRSS. Finally, the system design of the ZY-3 Satellite (China's first civil stereoscopic surveying and mapping satellite, to be launched in 2012) is introduced, which mainly include satellite technical specifications and strategies design based on these key technologies research.
1. Introduction
To improve China's independent capability of obtaining earth observation information, according to ‘National Science and Technology Development Plan (2006–2020)’ by the State Council, the high-resolution Earth Observing System has been regarded as one of the sixteen significant projects, which have priority on the China's future scientific and technological development. The mapping technologies of the domestic high-resolution remote sensing satellites (HRSS) are an important guarantee for China's geospatial frame and informationized surveying and mapping system, and indispensable for updates of land surveying and mapping as well as national geographic information.
The past decades have witnessed the great evolution from film-return satellites to transmission-type satellites, and from frame camera to single, double, or even three-line array CCD sensor. Spatial resolution of civil satellites increases from about 100 to 0.41 m, and time and spectral resolution have also been improved. The kinds of mapping satellites are getting richer, including optical satellites, SAR satellites, laser altimeter satellites, gravity satellites, navigation satellites, and others now.
Accordingly, satellite surveying technology has been promoted greatly. Work flow, product accuracy, and application range have been improved significantly. It was developed from mapping with control points to mapping with rare control points, even without control points, developed from stand-alone mapping to collaborative, seamless mapping, developed from the 1:250,000 scale to 1:5000 of mapping accuracy, developed from the domestic scope to global share for application range, and developed from simplex surveying products to the global geographic information acquisition and update. All these achievements are owed to the development of satellite surveying and mapping technology. Therefore, it is necessary to analyze and summarize the key technologies of surveying and mapping using HRSS.
2. Key technologies of surveying and mapping for HRSS
According to different application requirements, the varieties of the HRSS increase. High-resolution optical satellites are the major data source for geographic surveying and mapping at present, and they will be related and analyzed as follows.
For the HRSS, the stereo mapping accuracy is an important qualification for its performance. Based on the principle of photogrammetry, there are lots of factors influencing satellite mapping accuracy, including photographic baseline error, attitude error, image point measurement error, and camera interior orientation errors, such as principal distance or distortion error (Hu and Cao Citation2008). Except for the sensor itself, these errors are also related to the global positioning system (GPS), attitude control system, time synchronization system, payload system, and so on. Therefore, the corresponding key technologies of the HRSS, including sensor manufacture and design, attitude and orbit determination, geometric calibration, stereo mapping, and other aspects, are analyzed and summarized.
2.1. Design and manufacture of sensors
For HRSS, the design and manufacture of sensors is a fundamental factor influencing mapping accuracy. The topographic map scale is determined by satellite sensor resolution and accuracy. The visual resolution of a paper map for the human eye normally is about 0.07–0.1 mm; in other words, for topographic mapping, the resolution of the satellite image normally needs to be no larger than 0.1 mm on the map. For updates of topographic maps, the resolution needs to be 0.2 mm on the map at least. In addition, the angle design of multilines array CCD sensor and the scanning mode, related to the base to height ratio (B/H), are the important factors affecting mapping accuracy. Next, we briefly introduce them in the following section.
2.1.1. Spatial resolution of sensor
With the development of sensor manufacture technology, spatial resolution is getting higher, as shown in . For SPOT 4, the panchromatic band and multispectral band have resolutions of 10 and 20 m, respectively. SPOT 5 has two high-resolution geometrical (HRG) instruments that were deduced from the HRVIR of SPOT 4. They offer a higher resolution of 2.5 to 5 m in panchromatic mode and 10 m in multispectral mode. Recently, the spatial resolution of US commercial satellite sensors has been increasing rapidly. The panchromatic and the multispectral band of IKONOS-2 (launched 1999) have resolutions of 1 and 4 m, respectively. QuickBird-2, launched by the US Digital Globe company in 2001, can provide 0.61 m nadir-view panchromatic resolution and 2.44 m multispectral resolution. The panchromatic and multispectral images of Orbview-3 and Orbview-4 have resolutions of 1 and 4 m, respectively. As the next generation of IKONOS and OrbView-3, the GeoEye-1 satellite, launched in 2008, is a commercial satellite with the highest resolution and positioning accuracy in the world, with 0.41 m panchromatic resolution and 1.64 m multispectral resolution.
Table 1. Major surveying and mapping satellites
In addition, for some HRSS from other countries, KOMPSAT-2 acquires imagery in panchromatic mode at a resolution of 1 m and in multispectral mode across four bands (red, green, blue, near-infrared (NIR)) at a resolution of 4 m. The Israeli EROS-A offers a resolution of 1.8 m in the panchromatic mode, which can be improved to 0.9 m by sampling techniques. EROS-B satellite, launched in 2006, has 0.7 m panchromatic resolution. The Japanese Advanced Land Observation Satellite (ALOS) has a ground resolution of 2.5 m. The multispectral camera on the Advanced Visible and Near-Infrared Radiometer-2 (AVNIR-2) satellite comprises four bands at a ground resolution of 10 m. India's first mapping satellite, CARTOSAT-1 (namely IRS P5), was launched in 2005, with a resolution of 2.4 and 2.1 m for nadir-view, forward or backward views, respectively.
2.1.2. Design of camera angle and scanning mode
According to different demands, the satellite sensor has different designs. Sensors can be classified into two categories according to the quantity of line array: single-line array and multiline array, as shown in . Their technological characteristics are briefly introduced in the following sections.
Table 2. Technical Specifications of ZY-3
2.1.2.1. The single-line array CCD sensor
To obtain stereoscopic imagery, the satellites with single-line array CCD generally adopt the orbit regression or swing imaging modes, namely along-track stereoscopic imaging mode or cross-track stereoscopic imaging mode. Currently, typical single-line array satellites include the French SPOT 1–4, US IKONOS-2, QuickBird-2, Orbview-3, Orbview-4, GeoEye-1, Korean KOMPSAT-1, KOMPSAT-2, Israeli EROS, Canadian RapidEye, and so on. The US has always placed great emphasis on the development of the commercial HRSS. IKONOS-2 adopts stereoscopic mode to acquire image pairs along the track with a fine B/H, as rotation angle of the camera is set beforehand.
QuickBird-2 is another single-line array satellite made by the US Digital Globe company. QuickBird-2's imaging system can flexibly sway within the range of −25° to + 25°, and the block can be covered by stereo images in the along-track or cross-track mode. QuickBird-2 provides basic level stereo images without geometric correction. The panchromatic band has a resolution of about 0.78 m (with 30° inclination), and the multispectral band has a resolution of about 3.12 m. The B/H is between 0.6 and 2.0, within 0.9–1.2 in most cases, which is suitable for Digital Elavation Model (DEM) generation and ground features extraction.
2.1.2.2. The multiline array CCD sensor
To reduce the cost of the stereo imaging, multiple sensors are loaded on the satellite. Today, most mapping satellites adopt multiline array CCDs to get the along-track stereoviewing capability, including the French SPOT 5, Indian IRSP5, German MOMS-2P, and Japanese ALOS PRISM.
As a double-line array stereo mapping satellite developed by the Centre National d'Etudes Spatiales (CNES), SPOT 5 can obtain the along-track or cross-track stereo images. It is equipped with three kinds of payloads: the High-Resolution Stereoscopic (HRS) sensors, the HRG sensors, and the VEGETATION sensor. The HRG sensor is able to obtain cross-track stereo pairs by side-sway. HRS is composed of forward- and backward-view cameras. The B/H of along-track stereo is 0.84, which guarantees the accuracy of the generated DEM.
India's first stereo surveying and mapping satellite, namely IRS P5, is equipped with two identical panchromatic cameras. To achieve good elevation accuracy, the forward and backward optics are inclined by 26° and 5°, which corresponds to B/H=0.62. The time difference is only 52 s for taking the same scenery. This integrated stereoscopic mode can reduce the mutual occlusion in districts with great elevation differences, and the backward-view image can produce high-quality ortho-image products.
ALOS satellite is equipped with three sensors: Panchromatic Remote Sensing Instrument for Stereo Mapping (PRISM), AVNIR-2, and Phased Array Type L-band Synthetic Aperture Radar (PALSAR). The PRISM is the most advanced three-line array CCD mapping camera at present, with a 24° intersection angle of the three cameras and B/H=1.0.
For single-line array satellites, their image acquirement efficiency for cross-track stereo imaging declines due to weather. Their along-track stereo imaging is able to take photos of the same region within a short time, which greatly improves the efficiency of stereo image capture. However, it is difficult for flexible attitude control as well as the high stability.
For double-line array or three-line array satellites, it is easy to obtain wider ranges of stereo pairs along the track and remarkably improve the image quality of stereo imaging meanwhile. Three-line array CCD is the ideal stereo imaging mode, which has the advantages of stable constitution (along-track stereo, triple stereo), ideal B/H, and time consistency. It guarantees that high-accuracy target localization, high-quality DEM generation, acquisition and updates of GIS data, and mapping and revision of topographic and thematic maps.
2.2. Precise attitude determination
As the angular elements of exterior orientation, satellite attitude plays an important role in satellite mapping. If all other errors are ignored and the DEM data are known, the ground location of one satellite image point can be obtained by intersecting projection lines to the DEM. In that case, for satellites with the 600 km altitude, attitude error of 1 arc second leads to about ground location error of 3 m. Currently, to improve attitude accuracy and stability, most HRSS are equipped with both star sensors and gyroscopes. The star sensors are used to get absolute inertial attitude with low frequency, which has characteristics of highest accuracy and no drift. The gyroscopes can measure angular velocity with high frequency.
To improve three-axis attitude accuracy, generally, there are several star sensors and gyroscopes equipped on the satellites. QuickBird-2 adopts star sensors, gyroscopes, and reaction wheels to control its attitude, with the attitude stability less than 5.7×10−4°/s. GeoEye-1 employs the three-axis stabilization platform, with double-head star sensors, Inertial Reference Unit (IRU), and solar sensors to ensure its attitude determination accuracy, and its attitude jitter is 0.007″/s root mean square (RMS) (25–2000 Hz). Israel's EROS-A Satellite uses Earth sensors, solar sensors, gyroscopes, reaction wheels, and other instruments for its attitude control, with the attitude accuracy better than 0.1°, the stability less than 40 µrad/s, and its jitter less than 0.2 µrad. In comparison with EROS-A, the EROS-B added a star sensor and thus has even higher attitude accuracy. SPOT 5 employs star trackers and several groups of gyroscopes for satellite attitude control. The Indian IRS P5 also uses star sensors and gyroscopes to control satellite attitude, with an attitude stability less than 5×10−5°/s. To obtain high-accuracy attitude information, ALOS is equipped with forward-view, nadir-view, and backward-view star sensors (9″, 3σ). The forward- and backward-view ones operate, and the nadir-view one involves when suffering from moonlight interference. In addition, ALOS is also equipped with inertia gyroscopes and angular displacement sensors (with 0.012 RMS error). High-accuracy attitude control techniques ensures attitude accuracy remains 0.095° (3σ) and its attitude stability to reach 1.9×10−4°/5s when the data relay antennas are not in drive and 3.9×10−4°/5s when they are in drive. To determine in-flight attitude with star sensors and gyroscopes, the Extended Kalman Filtering approach, which is based on attitude kinematics or attitude dynamic equations to form systematic state equation, is often adopted. Through recursion of state value, error covariance, and observation information updates at measure time, state mean values and deviations are estimated while minimizing the estimated mean square error (Rao et al. Citation2002, Shan and Islam Citation2010).
Considering real-time requirements, the one-way time series filtering mode is often employed for in-flight attitude determination. To improve the attitude accuracy, the raw observed data of the star sensors and gyroscopes are recorded and downlinked to the ground station. The postprocessing, with a smoothing filter based on weighted covariance, is adopted. In the process, every smoothing process includes a forward Kalman filter, a backward Kalman filter as well as weighted covariance smoothing. With this postprocessing, ALOS attitude accuracy can reach 0.52″, which is much better than in-flight accuracy of 1.082″ (Iwata Citation2005).
Research on satellite attitude determination began relatively late in China. Compared with advanced level, there still exist obvious differences. The attitude accuracy and reliability cannot meet the demand of domestic HRSS, especially for the mapping without control points. The ZY-1 Satellite is China's first-generation transmission-type satellite for Earth observation; its attitude control system adopts a three-axis stable wheel-control system, while it consists of two infrared scanning sensors, two groups of orthogonally installed, rate-integrating gyroscopes, and sun sensors. When operating well, its control accuracies are obtained as follows: attitude accuracy is less than 0.15° (3σ), the attitude stability is less than 0.001° (3σ), and the attitude jitter is 0.0001° (1σ).
As a substitution, ZY-1 02 Satellite (ZY-1-02) is identical to ZY-1. ZY-1 02B satellite (ZY-1-02B), which was launched later, is much more advanced than the ZY-1 and ZY-1-02. To improve the geometric positioning accuracy (improved from 2.5 to 1 km), attitude accuracy was significantly enhanced by adding an infrared Earth sensor and a medium-accuracy star sensor.
2.3. Precise orbit determination
Satellite Orbit position is linear elements of exterior orientation for space photogrammetry, and their measurement errors are also directly related to the satellite mapping accuracy. There are four major kinds of high-accuracy satellite tracking techniques: the GPS, Satellite Laser Ranging (SLR), Doppler Orbitography and Radiolocation Integrated by Satellite (DORIS), and Precise-Range and Range-rate Equipment.
GPS is a new-generation satellite navigation positioning system which was developed by the US army, navy, and air-force in the late 1970s. There are 24 operating GPS satellites on orbit, with advantages of global coverage, all weather, constancy, and high-accuracy three-dimensional positioning. GPS has become an important means for precise satellite orbit determination and has been adopted by most HRSS such as IKONOS-2, QuickBird-2, GeoEye-1, KOMPSAT-1 and 2, and ALOS to capture data and obtain orbit information after data processing. To further enhance orbit positioning accuracy, ALOS is equipped with a dual frequency carrier phase tracking GPS receivers for precise position. The pseudo-range and phase data are transmitted to ground stations for the ground-based orbit determination. After postprocessing, the accuracy is less than 1 m, which is better than the real-time accuracy of 200 m.
SLR is a proven geodetic technique. In SLR, a global network of observation stations measures the round-trip flight time of laser pulses to satellites equipped with retroreflectors, which provides the accurate measurement between the satellite and the observation station. Initiated in the 1960s and developed over the past decades, SLR provides instantaneous range measurements of millimeter level. It is regarded as the most accurate tracking technique.
DORIS is a positioning system developed and monitored by CNES with participation of Institut Géographique National (IGN). It transmits to the satellite from 54 stations in the world and then obtains the satellite location by detecting and measuring the DORIS frequency shift of the signal. SPOT 4 and SPOT 5 employ the DORIS for orbit determination, whose position accuracy achieves 10 and 20 cm, respectively, after ground-processing (Li Citation2009).
China began the research on SLR and GPS in the early 1990s. Some institutions, such as Wuhan University, Shanghai Observatory, and the Institute of Geographic Surveying, had done lots of work on navigation positioning using GPS data (Zhao Citation2004). Research on precise orbit determination of Low Earth Orbit Satellite (LEOS) can be traced back to the end of the previous century. Since then, significant work has been done with observational data of SLR and GPS. A preliminary software system has been developed with the accuracy of 20 cm by kinematic orbit determination and the accuracy of about 10 cm by simplified dynamic orbit determination. However, the research achievements above have focused on methodological and theoretical exploration, and still have great gap with the world level in terms of theoretical systems and software integration.
2.4. Geometric calibration
The geometric parameters of satellite sensors are essential for high-accuracy positioning. Generally, these parameters can be calibrated before satellite launching, but it may vary as the space environment such as micro-gravity and temperatures, and so on change. Therefore, in-flight calibration is a very important technique for satellite surveying and mapping.
Satellite geometric calibration has a decades-long history. The French SPOT was one of the earliest satellites, whose high-accuracy geometric calibration had been successfully achieved. According to relevant data statistics, there are 21 calibration fields around the world for SPOT, which provide the reference data for in-flight calibration. After the launch of SPOT 5, the CNES employed the step-by-step calibration method that classifies uncalibrated parameters into different categories and calibrates them separately. The errors irrelevant with time are regarded as static errors, which include the look angle of each CCD, and pointing drift relative to the satellite body. The errors relevant with time are considered as the dynamic error, such as orbit position, attitude, and so on. After single static and dynamic calibrations, multiple stereo images are used for block adjustment to further reduce the impact of the remaining random errors on positioning accuracy.
Similarly, after the launch of IKONOS, the calibration group from NASA and other institutes completed the geometric calibration using the Lunar Lake, Railroad Valley, Dark Brooking, Denver, and other test fields. The calibration process is the same as that of SPOT 5, but it employed images with Modulation Transfer Function (MTF) target as calibration data for alignment calibration, and each MTF target is considered as ground control point (GCP) (Dial et al. Citation2003).
Geometric calibration of MOMS-2P can be divided into two parts: laboratory calibration and in-flight calibration. Self-calibration bundle adjustment with additional parameters is adopted for in-flight calibration. Multistrip images along track are chosen to form blocks for two kinds of stereoscopic imaging models. Block adjustment are used to further refine calibration parameters. The calibration process is as follows. First, self-calibration block adjustment is implemented for the single strip, and the parameters are resolved with all the GCPs. On the other hand, some GCPs are used to resolve parameter, and the other GCPs are exploited as check points to evaluate the accuracy of the digital terrain model. Based on calibration using the single strip, block adjustment with three strips is implemented. In this process, exterior orientation elements are modeled by image orientation method, and the impact of different intervals between orientation images on calculation precision is analyzed, and optimal calibration model is obtained ultimately (Kornus et al. Citation2000).
The ALOS calibration group exploited three test sites for calibration in Japan and Australia. Test site 1 covers one frame imagery and is used to calibrate lense distortion and the relative position of the line array CCD, and to verify the imaging stability of the camera in a short time. Test site 2 consists of three sub-fields along the track in sequence. The distances of them correspond to the forward-, nadir-, and backward-view of the three-line array in stereo imaging mode. The calibration based on forward-, nadir-, and backward-view images at the same time can help avoid the impacts of temperature or other factors on lenses, which can get more accurate relative position of the lenses. Test site 3 also consists of three ground control fields, which is used to analyze the impact of latitude change on the CCD geometric transformation within a relatively long time period (about 100 seconds), while imaging in the same latitude at the northern and the southern hemisphere, respectively (Tadono et al. Citation2004).
In the field of aerial photogrammetry, China established a geometric calibration system for aerial cameras at an early stage. It includes a high-accuracy ground field and a well-established calibration and test system. However, limited work has been done for satellite sensors, and also there has not been any test site specifically for satellite geometric calibration.
After the successful launch of CBERS1-02 in 2003, the China Resource Satellite Application Center organized 20 domestic research institutes to perform geometric calibration, and finally its ground positioning accuracy (RMS) reached 7 km. For CBERS2-03, launched in 2004, the Beijing Institute of remote information organized about 10 domestic institutes to complete radiometric and geometric calibration of CBERS2-03, with location accuracy of 200 m (RMS). In comparison with the advanced world level, the geometric calibration of China's high-resolution satellite lags behind (Zhang Citation2005).
2.5. Stereo mapping
Stereo mapping is the important procedure to generate products from satellite images. The geometric imaging models based on the technologies above, precise orbit and attitude determination, geometric calibration, and so on are constructed, and block adjustment with and without control points, respectively, is performed for image orientation. The main steps include imaging model construction and block adjustment. Imaging models include rigorous imaging model and rational function model (RFM). Block adjustment includes single sensor block adjustment and multisensor block adjustment. These are briefly introduced in the following sections.
2.5.1. Construction of imaging models
When a rigorous sensor model for high-resolution satellite images is constructed, it is necessary to take into account the geometric factors that cause image transformation in the imaging process, such as satellite orbit, satellite attitude, and camera parameters. According to different satellite imaging characteristics, with different assumptions, we construct the corresponding imaging geometric models based on the analysis and verification. The Orimoms model was formulated to process MOMS satellite images, as it adopts kinematic functions to describe the satellite orbit. In this model, the satellite position and attitude are described as time-related quadratic polynomials, and it is assumed that orientation parameters remain constant during the imaging process (Okamoto Citation1981). The Kratky model was validated by SPOT images first and then applied to the MOMS images. It assumes that the satellite is operating on an elliptical orbit, and the position of the sensor can be described as a function of the mean anomaly, M. Assumed that satellite attitude rate is a time-related cubic polynomial, and the satellite velocity is variable (Kratky Citation1989a, Citation1989b).
The SPOT Company published its geometric model in 2002, which exploited postprocessed orbit and attitude parameters as well as calibrated interior orientation elements (SPOT IMAGE Citation2002). To keep confidential, GeoEye Inc. (formerly Space Imaging) only provides the Rational Polynomial Coefficients (RPC) parameters calculated from the rigorous model for IKONOS (Dial and Grodecki Citation2002). The successful launch of IKONOS encouraged further research on RFMs, and many scholars made comparative studies between RFM and rigorous model. By analyzing the advantages and disadvantages of the RPC model, Madani indicated that it can be used for photogrammetry (Madani Citation1999). Based on the experiment using one SPOT image pair and NAPP image pair, Yang (Citation2000) concluded that the RPC model with a third or even second derivative can replace the rigorous model for SPOT images. Similarly, Grodecki (Citation2001) proved that the RPC model can replace the rigorous model to process single linear array pushbroom satellite images. In addition, QuickBird only provided the geometric model and RPC parameters for image as well.
2.5.2. Block adjustment
Recent years have witnessed the preliminary development and application of block adjustment techniques for satellite image.
For block adjustment for single sensor image, Chen and Lee (Citation1989) adopted an improved collinearity equation for the frame sensor as the basis of block adjustment, which is performed on SPOT stereo images from across track, with 28 GCPs and 22 check points. Finally, the planimetric and elevation accuracy is less than 10 m. Block adjustment based on the Hofmann model is conducted for MOMS-2P images by Kornus et al. (Citation1996), and the planimetric and elevation accuracy achieved was 1/3 pixel.
Bouillon et al. (Citation2002) adopted a Westin model to conduct block adjustment on SPOT 5 satellite images. With the geometric model developed by the Canada Remote Sensing Centre, CitationToutin (1995) obtained sub-pixel planimetric and elevation accuracy by conducting block adjustment experiments with Landsat-7 ETM+, SPOT 4 HRV, ASTER VNIR, RADARSAT, ERS, and other images on 25 control points. Zhang et al. (Citation2004) proposed a rigorous geometric model with affine transformation, based on which block adjustment is performed on 15 IKONOS-2 images, obtaining 1 m accuracy with five control points. The geometric models above are empirical models under approximate conditions. Consequently, they easily generated errors when regarded as the basis of block adjustment for single sensor image.
Block adjustment based on the RPC model was implemented for IKONOS-2 images by Grodecki and Dial (Citation2003), with 1 m accuracy with one control point and 7 m accuracy without any control points. In the same way, block adjustment based on the RPC model was carried out for single stereo pair of IKONOS-2 and Quickbird, 4 and 9 m accuracy without any control point and 1 m accuracy with one control point (Hanley et al. Citation2005).
3. Design of the ZY-3 Satellite
The ZY-3 Satellite (ZY-3) is China's first civil high-resolution, optical-transmission, stereoscopic mapping satellite, with multiple application for surveying, mapping, and resource investigation. ZY-3 travels a sun-synchronous orbit at an altitude of approximately 506 km and is capable of producing seamless imagery covering the earth's surface from 84 degrees southern latitude to 84 degrees northern latitude. ZY-3 image covers the global region every 59 days. The satellite attitude is determined by three star sensors, high-accuracy gyroscopes, and solar sensors, and so on, with the accuracy better than 0.01° (3σ). Postprocessing with the downlinked raw star sensor and gyroscope data can provide more precise attitude to fulfill mapping requirements. The orbit location can be obtained by the dual frequency GPS and SLR, with the position accuracy better than 10 m and the velocity accuracy better than 0.2 m/s. In addition, the raw GPS and SLR data are downlinked for postprocessing with refined mathematic models to get more precise position information. ZY-3 employs a three-line array camera system, which consists of forward-view, nadir-view, and backward-view TDI CCDs with certain intersection angle. Both the forward- and backward-view cameras have resolutions better than 4 m. The nadir-view resolution is greater than 2.5 m. The B/H is of 0.8–0.9, which is appropriate for the stereo surveying and mapping. Stereo pairs are generated by taking photo of the ground target from different perspectives, and the ground location can be obtained with precise interior and exterior orientation elements. It will accomplish the surveying and mapping for the first 1:50,000 scale map products and updates of 1:25,000 or even larger scale maps.
Based on the successful experiences of existing HRSS, a lot of researches such as the construction of calibration fields, precise orbit and attitude determination, in-flight calibration, and so on have been implemented in advance. It is of great benefit for the successful construction of ZY-3's ground application system.
4. Conclusions
Satellites surveying and mapping of China developed rapidly and have fundamentally taken shape in the past few decades, but in general, its development level cannot satisfy the national needs, and it still has a long distance to go compared with advanced global standards. Except for the laggard sensor manufacture techniques, satellite surveying and mappings techniques have also gradually outdated, and quantitative analysis and evaluation on satellite radiometric and geometric accuracy are insufficient. In addition, it is short of large-scale, highly reliable and accurate data-processing system, which caused the low efficiency of the satellite application currently.
Therefore, the research of these key techniques, including high-resolution sensor manufacture and testing, precise attitude determination, precise orbit determination, and in-flight geometric and radiometric calibration, and so on, should be strengthened. In this way, the integrated technical system will be established gradually, which ensures that domestic satellites can undertake national strategic tasks of geographic dynamic monitoring, global positioning, and update of 1:5000–1:50,000 topographic map databases.
Notes on contributors
Dr Tang Xinming is Professor, Doctoral Supervisor, and Deputy Director-General at the Satellite Surveying and Mapping Application Center (SASMAC, SBSM), and Chief Designer of the ZIYUAN-3 Satellite Application System. He studied at Nanjing University (B.Sc., Mapping and GIS), Netherlands Geo-Information Science and Earth Observation Institute (ITC) (M.Sc., Cadastral Mapping), and Netherlands Twente University (Ph.D., Geo-Information Science and Computer Application). His research covers geographical relation modeling in GIS, satellite photogrammetry, and related fields. He is responsible for the general demonstration and design of the ZIYUAN-3 Satellite, and leads core technology research on satellite image simulation, geometric calibration, and automatic image correction services, among other areas. He has published more than 90 papers in academic journals and international conference proceedings.
Junfeng Xie received the Ph.D. degree in photogrammetry and remote sensing from the Wuhan University, Wuhan, China, in 2009. He is currently with the Satellite Surveying and Mapping Application Center (SASMAC, SBSM) His is mainly engaged in satellite photogrammetry. It includes satellite attitude determination and Satellite geometric imaging model Construction research,etc.
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