ICESat-2 ATL03算法详细指南：全球定位激光脉冲原理

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本篇文档是关于ICESat-2项目算法的理论基础文件，专门针对全球定位光子（ATL03）的测量和处理。ICESat-2是NASA的一个重要任务，利用其ATLAS仪器进行精密的地球观测，主要依靠光子计数激光雷达技术。该设备发射绿色（532纳米）激光脉冲，以每秒10,000次的频率在大约500公里高的冻结轨道上扫描地球表面，每0.7米就产生一次发射。 ATL03的主要任务包括测量光子往返地球的时间，这提供了关于地球表面到卫星的距离信息，进而推算出高程数据；记录光子发射时ATLAS的指向矢量，有助于理解激光束的路径和反射方向；以及卫星在空间中的精确位置，这对于测绘和遥感应用至关重要。通过六个独立光束的产生，ATLAS能够获取更精细的地表细节和云层信息。与早期的全波形激光雷达系统（如ICESat上的GLAS仪器）相比，这种方法依赖于对激光脉冲的精确分析，而非单个脉冲的完整波形。数据处理和分析由多个专家团队负责，包括Tom Neumann、Anita Brenner等人，他们均来自NASA Goddard Space Flight Center的特定代码部门，确保了数据的质量和科学准确性。 ATL03版本005是在2021年秋季发布的，作为ICESat-2科学办公室受控文档，任何更改都需经过科学发展团队的认可。这份文档详细阐述了从接收光子到将其转化为地理定位信息的整个过程，是理解ICESat-2如何提供全球高精度地形、气候和环境数据的关键文档。通过ATL03，科学家和研究人员可以利用这些数据进行高精度的地球表面测绘，监测海平面上升，研究冰川变化，以及评估地表反射率和植被覆盖等。这些数据对于气候变化研究、地球系统模型的验证和改进，以及灾害预警等领域具有重大意义。此文档深入探讨了ICESat-2如何利用先进激光技术在全球范围内进行高精度的地理测量，为科学研究和应用提供了强大的工具。

ICESat-2 Algorithm Theoretical Basis Document for Global Geolocated Photons (ATL03)

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Release Date Fall 2021

xvi

List of Tables

Table Page

Table 5-1. Input Variables for Photon Classification Algorithm. ................................................. 54

Table 5-2. Parameters Needed to Drive the Algorithm; Input Parameters. .................................. 60

Table 5-3. Parameters Calculated Interally Within the Algorithm. .............................................. 65

Table 5-4. Parameters Output from Signal Finding Algorithm. ................................................... 65

Table 6-1. Table of Geophysical Corrections and Reference Model Sources for ICESat-2. ....... 98

Table 6-2. Ocean Tidal Models Currently Available.................................................................. 101

Table 6-3. Performance Order of Tide Models Based on RSS over Main Constituents ............ 101

Table 7-1. Transmitted Pulse Energy Parameters. ...................................................................... 115

Table 7-2. Transmit Pulse Parameters. ....................................................................................... 116

Table 7-4. Altimetric Histogram Parameters. ............................................................................. 125

Table 7-5. Table to relate ph_id_channel to a photon’s path through ATLAS. ......................... 127

Table 7-6. Beam mapping when sc_orient == 1 (forward). ....................................................... 128

Table 7-7. Beam mapping when sc_orient == 0 (backward). .................................................... 128

Table 10-1. ATL03 Output Parameter Table. ............................................................................. 175

ICESat-2 Algorithm Theoretical Basis Document for Global Geolocated Photons (ATL03)

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Release Date Fall 2021

1.0 INTRODUCTION

This section introduces the ICESat-2 mission, the measurement concept of its sole instrument

(ATLAS, the Advanced Topographic Laser Altimeter System), and the family of ICESat-2 data

products.

1.1 Background

The ICESat-2 observatory and ATLAS instrument use a photon-counting lidar and ancillary

systems (i.e. GPS and star cameras) to make three primary measurements: the time of flight of a

photon from ATLAS, to the Earth, and back to ATLAS; the pointing vector at the time a photon

is transmitted by ATLAS; and the position of ICESat-2 in space at the time a photon is recorded

by ATLAS. This measurement approach is fundamentally different from a full-waveform lidar

system (such as the 1064-nm GLAS instrument on ICESat). The ATLAS instrument transmits

green (532-nm) laser pulses at 10 kHz; the spacecraft velocity from the ICESat-2 nominal ~500-

km frozen orbit altitude yields one transmitted laser pulse every ~0.7 meter along ground tracks.

Each transmitted laser pulse is split by a diffractive optical element in ATLAS to generate six

individual beams, arranged in three pairs (Figure 1-1). The beams within each pair have different

transmit energies (‘weak’ and ‘strong,’ with an energy ratio between them of approximately 1:4)

and are separated by 90 meters in the across-track direction. The beam pairs are separated by

~3.3 kilometers in the across-track direction, and the strong and weak beams are separated by

~2.5 kilometers in the along-track direction. Figure 1-1 shows the idealized beam and footprint

pattern for ICESat-2.

Figure 1-1. ATLAS Idealized Beam and Footprint Pattern.

The left panel (Figure 1-1) shows the beam pattern for ICESat-2, while the right panel shows the

instantaneous footprint pattern generated by each transmitted laser pulse from ATLAS. Light

green circles indicate footprints from the relatively low energy (weak) beams, while the dark

green circles indicate footprints from the relatively high-energy (strong) beams. As the

ICESat-2 Algorithm Theoretical Basis Document for Global Geolocated Photons (ATL03)

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Release Date Fall 2021

observatory moves in the along-track direction, the aggregation of overlapping footprints form a

ground track on the Earth’s surface.

Approximately 10

photons begin the journey from ATLAS, travelling through the atmosphere

to reflect off the Earth’s surface, return through the atmosphere and back into the ATLAS

telescope.

For highly reflective surfaces and clear skies, on the order of ten signal photons from a single

strong beam are expected to be recorded by ATLAS for a given transmit laser pulse. At the same

time, background photons from sunlight at the same 532-nm wavelength may be arriving at the

detector, and some of them will also be recorded by ATLAS. Any photon that ATLAS records

an arrival time for is called a photon event, regardless of the source of the photon. The number of

photon events recorded by ATLAS depends on the geometry and reflectance of the Earth’s

surface, solar conditions, and on scattering and attenuation in the atmosphere. The number of

returned photon events varies from near zero photon events per shot over very dark non-

reflective surfaces, up to twelve photon events per shot over very reflective surfaces.

In order to reduce the volume of data downlinked to Earth, ICESat-2 uses on-board flight

software to identify and downlink data from those photon events most likely to represent

returned photons from the laser pulse while also providing data on the atmospheric conditions.

Given the 10-kHz laser pulse repetition rate, there are many transmitted laser pulses en route to

and from Earth at any point in time. Transmitted laser pulses are separated in flight by ~30

kilometers in one-way travel. As such, there is an inherent height ambiguity of ~15 kilometers in

received photon events. Consequently, ICESat-2 can only characterize the lowest ~15 kilometers

of the Earth’s atmosphere. The on-board software counts photon events and generates a

histogram spanning the lowest ~14 kilometers of the atmosphere with 30-m vertical bins. These

atmospheric histograms aggregate the number of photon events over four hundred consecutive

laser transmit pulses (an atmospheric histogram is generated every 0.04 seconds, spanning 280

meters of along-track distance). Atmospheric histograms are downlinked for the three strong

ATLAS beams.

The volume and rate of photon events is large enough that ATLAS cannot assign unique time

tags to every received photon event and downlink the relevant information. Instead, the flight

software sets a range window of at least 500 meters and not more than 6,000 meters within

which detected photons are time tagged and become photon events. The width of the window

primarily depends on the surface type (e.g. ocean, land ice, land) as well as the topography

(Leigh et al., 2014). Within the range window, ATLAS attaches time tags for received photons

and generates altimetric histograms of these events. The on-board software uses these histograms

to identify the surface and specify which photon event data are downlinked to Earth for each

beam. The band of photon time tags downlinked to Earth is called the telemetry band. The width

of the telemetry band of each beam is potentially different, and is described fully in the ATLAS

Science Receiver Algorithm Description document.

The ATL02 ATBD contains a description of how photon times of flight are calculated. The

pointing vector and observatory position in space are described by the ATBDs for Precision

Pointing Determination (PPD), and Precision Orbit Determination (POD), respectively.

ICESat-2 Algorithm Theoretical Basis Document for Global Geolocated Photons (ATL03)

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Release Date Fall 2021

While the lower-level data products typically work with individual photon events, higher-level

geophysical data products work with aggregations of photons in order to determine the

ellipsoidal height of the Earth, canopy height and structure, and other quantities of geophysical

interest. To learn more about these higher-level data products, refer to their ATBDs.

1.2 Data Product Overview

The family of ICESat-2 data products and the connections between them are shown in Figure

1-2. The ATL01 algorithm reformats and unpacks the Level 0 data from ICESat-2, then converts

it into engineering units. The ATL02 processing applies instrument corrections to these data. For

example, photon event time tags are corrected for the effects of temperature and voltage

variations on the ATLAS electronics, and biases are removed from timing and pointing

measurements. The Precision Orbit Determination and Precision Pointing Determination use data

from ATL02 to determine the position of the ICESat-2 observatory as a function of time and the

pointing vector of the observatory as a function of time.

ATL03 combines the data products of POD, PPD, and ATL02 to produce a Level 2 product

containing geolocated ellipsoidal heights for each time tagged photon event downlinked from

ATLAS. These heights are corrected for several geophysical phenomena (e.g. atmospheric

refraction, tides) and are classified either as likely signal photon events or likely background

photon events.

Atmospheric data products draw the raw atmospheric profiles for each strong beam from ATL02.

ATL04 provides normalized relative backscatter profiles and ATL09 produces calibrated

backscatter profiles, atmospheric layer heights, and related atmospheric parameters.

All Level 3A data products draw from the geolocated photon heights in ATL03 and the

atmospheric parameters from ATL09. Along-track land ice ellipsoidal heights are provided in

ATL06, along-track sea ice and polar ocean heights are provided in ATL07, and along-track

terrestrial ellipsoidal height and related metrics for vegetation heights are provided in ATL08.

Sea ice freeboard for the Arctic and Antarctic seas and associated parameters are in ATL10.

Ocean heights are provided in ATL12, while inland water heights are in ATL13.

Level 3B data products are gridded products, drawing from the along-track products of Level

3A. ATL11, 14, and 15 are gridded land ice products corresponding to land ice height time

series, annually gridded land ice heights, and gridded land ice height change. Sea ice gridded

data for the Arctic and Antarctic are provided in ATL20 and 21. Gridded terrestrial data is

provided in ATL18 while the gridded mean sea surface heights are in ATL19. Lastly, weekly

and monthly gridded atmospheric data products are provided in ATL16 and 17.

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ICESat-2 ATL03算法详细指南：全球定位激光脉冲原理

ICESAT-2 +ATL03 + ATL08

ICESAT数据产品介绍

算法文档,来看看吧

算法.pdf

算法pdf文档合集数据结构

ICESat2_ATL03g_ATBD_r002.pdf

ICESat2_ATL03_ATBD_r004.pdf

ICESat2_ATL03A_ATBD.pdf

ICESat2_ATL03_ATBD_ATL03_GblGeoPhotons_03Mar2020r003.pdf

ICESat2_ATL06_ATBD_r004.pdf

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