ATLAS/ICESat-2 L3A Calibrated Backscatter Profiles and Atmospheric Layer Characteristics, Version 6
Data set id:
ATL09
DOI: 10.5067/ATLAS/ATL09.006
This is the most recent version of these data.
Version Summary
Version Summary
Changes for Version 6 are as follows:
- Modified blowing snow detection algorithm to reduce false positive detections often seen in daylight
- Added and modified the blowing snow confidence values (bsnow_con) to include new descriptions and changed the parameter from a one-byte to a two-byte integer value
- Added four values to the layer attribute parameter (layer_attr)
- Added a new parameter called clear air precipitation top height (cap_h) that denotes the top height of clear air precipitation that reached the ground
- Replaced the ANC32 surface reflectance map (now based on three years of ICESat-2 surface reflectance measurements instead of two) to fill in gaps
- Changed bs_quartile to bs_quantile in ATL09 and related code
- Modified code to use density matrix 1 instead of density matrix 2 when computing layer densities
- Implemented a third pass of the density dimension algorithm to reduce the effect of noise in creating false layers
- Updated the ANC45 cloud/aerosol discrimination table to increase the accuracy of detected layers
Overview
This data set (ATL09) contains calibrated, attenuated backscatter profiles, layer integrated attenuated backscatter, and other parameters including cloud layer height and atmospheric characteristics obtained from the data. The data were acquired by the Advanced Topographic Laser Altimeter System (ATLAS) instrument on board the Ice, Cloud and land Elevation Satellite-2 (ICESat-2) observatory.
Parameter(s):
LIDAR BACKSCATTER
Platform(s):
ICESat-2
Sensor(s):
ATLAS
Data Format(s):
HDF5
Temporal Coverage:
13 October 2018 to present
Temporal Resolution:
- 91 day
Spatial Resolution:
- Not Specified
Spatial Reference System(s):
WGS 84
EPSG:4326
Spatial Coverage:
N:
90
S:
-90
E:
180
W:
-180
Blue outlined yellow areas on the map below indicate the spatial coverage for this data set.
Strengths and Limitations
Strengths
- Lidar and radar are the only remote sensing techniques that can capture the vertical distribution of clouds at a high resolution; likewise, aerosols can only be resolved with lidar. This product provides the vertical distribution of clouds and aerosols at 280 m along-track and 30 m vertical resolutions from the surface to 14 km altitude with global coverage.
- This is the only product to provide surface reflectivity over land and ocean at 532 nm.
- This is the only spaceborne lidar providing three vertical profiles of calibrated, attenuated backscatter using three separate laser beams.
- Along with Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), this product provides detailed measurements of blowing snow layer height and optical depth but provides better spatial coverage than CALIPSO.
- The product has excellent signal to noise ratios during the night and low sun angles.
- Unlike CALIPSO, ICESat-2 is not in a sun-synchronous orbit which allows the data to be used for studies of diurnal changes of cloud and aerosol properties.
- This is the only product that provides clear-air precipitation (diamond dust) occurrence over Antarctica.
Limitations
- The backscatter profiles span a limited height range — from the surface to 14 km altitude — and are available at nadir directly below the spacecraft (no swath width).
- Backscatter (clouds/aerosol) at altitude h, where h > 15 km, is folded down and added to the backscatter present at an altitude of h - 15 km (Palm et al., 2021).
- The signal between 14 and 15 km is not downlinked.
- Daytime signal to noise is low due to solar background noise. While this impacts layer detection, most clouds are detected but only very thick aerosol can be detected during daytime.
- Very optically thin aerosol layers (< 0.05) may not be detected.
- Calibration is generally very good at night, but during day/night transition (i.e., twilight) calibration error may exceed 10%.
- Thick aerosol may be mistakenly classified as cloud.
- Very thin clouds in the polar regions (i.e., very optically thin ice crystal clouds or diamond dust) may be classified as aerosol.
- The signal is completely attenuated below clouds of optical depth greater than 3–4.
Data Access & Tools
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General Questions & FAQs
This article covers frequently asked questions about the NASA NSIDC DAAC's Earthdata cloud migration project and what it means to data users.
This short article describes the customization services available for ICESat-2 data using Earthdata Search.
How to Articles
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Harmony API Quickstart Guide: Customizing NASA NSIDC DAAC data in Earthdata Cloud
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