In situ timing and pointing verification of the ICESat altimeter using a ground‐based system

Magruder, Lori A.; Silverberg, E. C.; Webb, C. E.; Schutz, B. E.

doi:10.1029/2005gl023504

Cited by 32 publications

(18 citation statements)

References 7 publications

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“…The aerophotogrammetric DEM and ICESat (DI ) resulted in the smallest shift vector (≈3 m) and an RMSE (3.6 m) of stable terrain after two iterations. We expect the aerophotogrammetric DEM to be of the highest quality and accuracy, thus the impressive coherence with ICESat further confirms previously published ICESat horizontal and vertical accuracies (Fricker et al, 2005;Luthcke et al, 2005;Magruder et al, 2005;Shuman et al, 2006;Brenner et al, 2007). For the other 5 comparisons, the SPOT5-HRS DEM compared better than the ASTER, with a shift vector Before After Fig.…”

Section: Universal Co-registration Correctionsupporting

confidence: 71%

Co-registration and bias corrections of satellite elevation data sets for quantifying glacier thickness change

2011

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Abstract.There are an increasing number of digital elevation models (DEMs) available worldwide for deriving elevation differences over time, including vertical changes on glaciers. Most of these DEMs are heavily post-processed or merged, so that physical error modelling becomes difficult and statistical error modelling is required instead. We propose a three-step methodological framework for assessing and correcting DEMs to quantify glacier elevation changes: (i) remove DEM shifts, (ii) check for elevation-dependent biases, and (iii) check for higher-order, sensor-specific biases. A simple, analytic and robust method to co-register elevation data is presented in regions where stable terrain is either plentiful (case study New Zealand) or limited (case study Svalbard). The method is demonstrated using the three global elevation data sets available to date, SRTM, ICESat and the ASTER GDEM, and with automatically generated DEMs from satellite stereo instruments of ASTER and SPOT5-HRS. After 3-D co-registration, significant biases related to elevation were found in some of the stereoscopic DEMs. Biases related to the satellite acquisition geometry (along/cross track) were detected at two frequencies in the automatically generated ASTER DEMs. The higher frequency bias seems to be related to satellite jitter, most apparent in the backlooking pass of the satellite. The origins of the more significant lower frequency bias is uncertain. ICESat-derived elevations are found to be the most consistent globally available elevation data set available so far. Before performing regional-scale glacier elevation change studies or mosaicking DEMs from multiple individual tiles (e.g. ASTER GDEM), we recommend to co-register all elevation data to ICESat as a global vertical reference system.

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Section: Universal Co-registration Correctionsupporting

confidence: 71%

Co-registration and bias corrections of satellite elevation data sets for quantifying glacier thickness change

2011

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“…The results show the range errors from frequency change are <1 cm [ Sun et al , 2004]. The accuracy of the GLAS measurement time stamps has been evaluated by registering the arrival time of laser pulses from GLAS at a ground based detector array [ Magruder et al , 2005] and the errors were found to be <3 usec.…”

Section: On‐orbit Science Measurementsmentioning

confidence: 99%

Geoscience Laser Altimeter System (GLAS) on the ICESat Mission: On‐orbit measurement performance

Abshire

Sun

Riris

et al. 2005

Geophysical Research Letters

367

242

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[1] The GLAS instrument on NASA's ICESat satellite has made over 904 million measurements of the Earth surface and atmosphere through June 2005. During its first seven operational campaigns it has vertically sampled the Earth's global surface and atmosphere on more than 3600 orbits with vertical resolutions approaching 3 cm. This paper summarizes the on-orbit measurement performance of GLAS to date. Instrument Description and Ground Testing[2] The Geoscience Laser Altimeter System (GLAS) is a new generation space lidar developed for the Ice, Cloud and land Elevation Satellite (ICESat) mission [Schutz et al., 2005]. The GLAS instrument combines a 3 cm precision 1064-nm laser altimeter with a laser pointing angle determination system and 1064 and 532-nm cloud and aerosol lidar [Zwally et al., 2002]. GLAS was developed by NASA-Goddard as a medium cost and medium risk instrument.[3] GLAS uses the 1064-nm laser pulses to measure the two way time of flight to the Earth's surface. The instrument time stamps each laser pulse emission, and measures its emission angle relative to inertial space, the transmitted pulse waveform and the echo pulse waveform from the surface. GLAS also measures atmospheric backscatter profiles. The 1064-nm pulses profile the backscatter from thicker clouds, while the 532-nm pulses use photon-counting detectors to measure the height distributions of optically thin clouds and aerosol layers [Abshire et al., 2003]. A GPS receiver on the spacecraft provides data for determining the spacecraft position, and provides an absolute time reference for the instrument measurements and the altimetry clock.[4] Before launch, GLAS measurement performance was evaluated with ''inverse lidar'' called the Bench Check Equipment (BCE). The BCE also monitored the transmitted laser energy and the other critical instrument measurements [Riris et al., 2003]. Before launch, the three GLAS lasers were qualified [Afzal et al., 2002] and fired a total of 427 million shots, or 11% of the planned orbital lifetime. This pre-launch testing also uncovered a few issues. The co-alignment of the laser beams to the receiver field of view was found to vary more than expected, with instrument temperature and orientation. Three of the eight 532-nm detectors failed during instrument vacuum testing. Laser 3 also showed an unexplained small drop in its 532 nm energy. Unfortunately, due to project deadlines, it was not possible to correct these issues before launch. Space Operation of Lasers and Laser Energy History[5] After the ICESat launch, GLAS Laser 1 started firing on February 20, 2003, and was operated continuously through the Laser 1 campaign. The GLAS 1064-nm measurements showed strong echo pulses from the surface and cloud tops and better than expected atmospheric profiles. Operation of the 532-nm detectors was delayed. Figure 1 shows the 1064 and 532-nm energy histories to date for all lasers, with Laser 1 shown in red. After day 10, Laser 1 showed unusual and faster than expected energy decline, and it failed on day 38. NAS...

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“…For validation, we assume that both the GLAS range measurement and its pointing direction may be in error but that the orbital position has negligible error, based on state of the art orbit estimation [ Schutz et al , 2005]. Data time tags have been validated to a few microseconds [ Magruder et al , 2005] and are also a negligible error source. To validate both range and pointing throughout the satellite lifetime, GLAS measurements are required over independently‐surveyed, unchanging topography for which a change in pointing produces a change in range.…”

Section: Introductionmentioning

confidence: 99%

ICESat range and mounting bias estimation over precisely‐surveyed terrain

Martin

Thomas

Krabill

et al. 2005

Geophysical Research Letters

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Prior to the launch of the Geoscience Laser Altimeter System (GLAS) on the Ice, Cloud and land Elevation Satellite (ICESat) in January 2003, topographic surveys were made by NASA's Airborne Topographic Mapper (ATM) over regions of the western United States and the Antarctic Dry Valleys to support calibration and validation of the range and pointing errors of GLAS lasers. Surveyed areas included terrain with large slopes, allowing pointing‐bias estimation with as little as a few seconds of ICESat data. Range errors over sloping irregular surfaces are calculated by computing the expected GLAS return waveform and comparing it with the actual waveform. We conclude that the range bias is less than 2 cm and that pointing errors for the best available data set (Laser 2a) have rss errors less than 2 arcsec.

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In situ timing and pointing verification of the ICESat altimeter using a ground‐based system

Cited by 32 publications

References 7 publications

Co-registration and bias corrections of satellite elevation data sets for quantifying glacier thickness change

Co-registration and bias corrections of satellite elevation data sets for quantifying glacier thickness change

Geoscience Laser Altimeter System (GLAS) on the ICESat Mission: On‐orbit measurement performance

ICESat range and mounting bias estimation over precisely‐surveyed terrain

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