ICESat-2: SIMPL Documentation
SIMPL Data Release 5
Release 5 of the 2015 SIMPL data is being made available. A large amount of the data acquired in Greenland is now posted online. Improvements in the data and limitations are described in detail on slides 3 to 6 in SIMPL_2015_Rel5_Documentation_v1.1.
Improvements over Prior Releases
Geolocation accuracy has been improved by including precise attitude and timing biases. For flat surfaces the residual elevation and horizontal errors for each of the 16 data channels are ~ 1 cm and 10 cm level per 1 deg angle off nadir, respectively. Absolute range biases for each of the 16 channels have also been applied. Based on initial analysis the between-channel elevation accuracies are at the decimeter level. Confirmation of the absolute accuracy with respect to an independent elevation source is pending.
Parameters documenting the impulse response pulse position, width and amplitude have been improved and information on their time variability has been added.
Cautions on the use of Release 5 Data
For studies of penetration into snow, ice and water several objectives have not been met in Release 5. Those objectives are: (1) elevation accuracy between the four channels on each of the four beams at the cm-level, (2) monitoring time variability of the channel elevation biases and (3) providing a of first photon bias calibration at the cm-level relating elevation offset to probability of detection. Work is on-going to achieve these objectives.
Monitoring time-varying impulse response pulse shapes for each of the 16 channels yields inconsistent results. Therefore the reported pulse shapes included in this release cannot be used with confidence. Work is on-going to provide robust pulse shapes for each of the channels.
Signal amplitudes are relative measurements. Probabilities of detection and signal to noise ratios are derived from raw photon counts. They have not been calibrated to account for instrumentation differences between channels. Scale factors are being determined to normalize the amplitude parameters to enable comparison between channels.
There is a time reference discrepancy in some auxiliary groups that causes misalignment with other time-series data. The computation of their time that allows the data to be aligned is provided in the Release 5 documentation, slide 6.
Time of day errors have been identified for a number of files introducing data gaps. For some files the time errors have been corrected and the data is on-line. Work is on-going to correct some of the other files which will be posted as they become available. If you are missing critical data please let us know. Files for July 21 cannot be corrected and will not be posted. It has not been determined if files for July 23 and August 11 can be corrected.
As indicated above, improvements to address these cautions are being developed. Information on those improvements will be posted on the ICESat-2 SIMPL data distribution web site as they become available. For scientific analyses please verify you are working with the latest release of the data by referring to the distribution site. Refer to the release notes and standard data product descriptions for information on changes in data attributes, quality and/or processing methods if future releases are distributed.
Please email David Harding (firstname.lastname@example.org) with a copy to Tom Neumann (email@example.com) and David Hancock (firstname.lastname@example.org) regarding any quality issues you identify while working with the data or if you have questions about these data. This will be helpful to us as we continue to improve the SIMPL data products.
Caution on usage of SIMPL Data Release 2
Extensive work has been done to produce geolocated SIMPL data in an HDF5 format similar to the MABEL data Release 8. However this work is preliminary. For each of the three deployments (2009, 2010, 2011) range and angle biases have been established from only one segment of flight data. The stability of the bias results within and between flights during a deployment has not been evaluated in detail, so the geolocated data are NOT considered to be fully calibrated. In addition, unlike MABEL processing which uses a Digital Elevation Model to select a data window encompassing the surface, SIMPL processing uses a surface tracking approach. Not all data has been examined to determine if the extracted data window includes the surface; in particular surface tracking may fail in the presence of broken clouds below the aircraft.
Improvements in geolocation and/or surface tracking may be developed leading to later data releases. Please verify you are working with the latest release of the data by referring to the ICESat-2 SIMPL data distribution site. Refer to the release notes and standard data product descriptions for information on changes in data attributes and/or processing methods in future releases.
Data may not be reproduced or distributed without including the Citation For External Publication (below). Data may not be distributed in an altered form without the written permission of David Harding and the ICESat-2 Project Science Office.
Citation For External Publication
Development of the SIMPL instrument was funded by the NASA Earth Science and Technology Office Instrument Incubator Program. Data collection and processing to Level 1 was performed by David Harding, Philip Dabney, Susan Valett and Aleksey Vasilyev at NASA/GSFC and Kyle Krabill at NASA/WFF. In 2009 and 2010 NASA/GRC Aircraft Operations provided flight support and funding was provided by ESTO/IIP and the IRAD Fund and ICESat-2 Project Science Office at NASA/GSFC. In 2011 the NASA/WFF Aircraft Office provided flight support and funding was provided by the NASA Cryosphere and Earth Surface and Interior Programs. Level 2 data was produced by the ICESat-2 Project Science Office.
Release 5 Documentation
- Release 5 Data Product Documentation and Instrument Description
- Greenland 2015 Flight Report
- Publication on Instrument Design and Performance for Greenland Campaign
The SIMPL Data Dictionary describes the structure of the SIMPL data.
The SIMPL file naming conventions are as follows:
Release 2: simpl_l2a_yyyymmddthhmmss_yyyymmddthhmmss_rrr_v.h5
Release 5: simpl_l2a_yyyymmddthhmmss_rrr_v.h5
yyyymmddthhmmss is the start or end date and time in hours, minutes, and seconds of the data.
rrr is the release number of the data.
v is the version number of the data for this release.
The link below will take you to a page where you can select SIMPL flight data by date as well as download descriptions.
The link below will take you to pages where you can download HDF5 files for selected SIMPL flights.