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The CPR began collecting research data on June 2, 2006. The radar entered a hibernation state in August 2020, but a return to operations is expected in late 2021.

Through the years, a number of changes to radar operations have occurred that users should keep in mind, and there are several multi-month periods where the radar was not operating. The next section highlights some of these important dates.

Between 2006 and the present, a number of changes have occurred to the operation of the radar. Key dates when these changes occur are used to divide the mission into a number of epochs; see below for a comprehensive list.
Show Epoch Info Probably the most important change is the use of Daylight-Only Operations (DO-Op) since October 27, 2011.

Some of the most important dates to keep in mind:

• 2011-04-17: Radar goes offline due to a battery anomaly.
• 2011-10-27: Radar returns to operations under a new operating paradigm whereby the radar only operations in the sunlit portions of the orbit. All CloudSat data since this date have been daytime-only.
• 2017-12-05: Radar goes offline. In the following months, CloudSat exits the A-Train after a reaction wheel anomaly.
• 2018-05-18: Radar resumes collecting data as it drifts to a new orbit.
• 2018-10-10: CloudSat enters the C-Train, reestablishing formation flying with CALIPSO.
• 2020-08-27: The CPR experiences a voltage anomaly. The radar has been offline since then, but plans are underway to return to operations in late 2021.

Data products are organized by Level. All Level 0, 1B, 2B, and 2C products are “orbit-level” products; they contain vertical cross sections relative to the CPR ground track for one revolution around Earth (one granule). Level 3 products, by contrast, are gridded and applicable to the entire globe over a specified time period.

• Level 0: Instrument data at full resolution, processed to sensor units. Not recommended for most users.
• Level 1B: Calibrated backscatter power as a function of distance from the radar. Most users should use the Level 2 product named “2B-GEOPROF” instead, since it contains radar reflectivity.
• Level 2B and 2C: Our standard data products, including radar reflectivity; as well as derived products such as cloud mask, water content, precipitation, and radiative fluxes.
• Level 2D: Data products we disseminate that were produced by external organizations.
• Level AUX: Various auxiliary datasets, subsampled to the CPR track, that are used to produce Level 2B/C products, or provide useful extra information to users.
• Level 3: Gridded data derived from Level 2B and 2C products.

A brief description of our core Level 2 products follows:

Product	Core Contents
2B-GEOPROF	Radar reflectivity, cloud mask
2B-GEOPROF-LIDAR	Combined CPR+CALIOP cloud mask
2B-CLDCLASS	Cloud classification
2B-CLDCLASS-LIDAR	Cloud classification supplemented by CALIOP lidar
2B-CWC-RO	Cloud liquid/ice water content and microphysical parameters
2B-CWC-RVOD	Cloud liquid/ice water content and microphysical parameters, constrained by MODIS optical depth
2B-FLXHR	Radiative flux/heating rate profiles
2B-FLXHR-LIDAR	Radiative flux/heating rate profiles supplemented by CALIOP lidar
2C-ICE	Cloud ice water content
2C-PRECIP-COLUMN	Precipitation type and occurrence
2C-RAIN-PROFILE	Rain rate profiles
2C-SNOW-PROFILE	Snow rate profiles
2C-TB94	94 GHz brightness temperature

Example quicklooks from some of our products follow. In these cross sections, the horizontal axes are time (or distance) and the vertical axes are height.

Details about our products can be found by using the Data Products pull-down menu at the top of this page, and selecting the “Level” of the product you want to find out more about.

There are several ways to find the data using this website. The easiest way to locate the Level 2 data you need is to utilize the data ordering system, which allows you to search for data by either date, granule number, or geographic location (coming soon). The first step is to click the “Orders” tab at the top of this screen, then select “New Orders”. Login with your username and password, or if you don’t already have one, you can create a new account from here.

• If you are interested in data from a certain date or range of dates, use the Search by Date tool. Enter a start data and end date in the appropriate boxes (either using the calendar selection tool, or by typing a date in the format YYYY-MM-DD), then select a product and version. In most cases, users will want to choose the latest version.

• If you already know the granule number containing the data you want to retrieve (perhaps from browsing through Quicklooks images), use the Search by Granule tool. Enter a first and last granule number, then select a product and version. In most cases, users will want to choose the latest version.

• A geographic selection tool is currently in development. This will allow you to select data relevant to satellite overpasses of the geographic region you select. Until this tool is completed, please use the date or granule selection tool instead.

Once search parameters are entered, select “Search”. Any granules matching your search parameters will be displayed in a list, which may extend over multiple pages.

You might wish to note the granule numbers and use the Quicklook tool to examine the data in these files.

If you are wish to download only some of the data returned by your search, either:

• Select “Add to Cart” next to an individual granule of interest
• Select the tick boxes next to multiple granules of interest, then select “Add Selected”,

When you are done, select “View cart” at the top of the page, and then “Submit Order” when you are satisfied with your selections.

If you wish to download all of the data returned in the search, select “Add All” to add all granules to the cart, then select “Submit Order”.

In brief, every CloudSat granule contains information in the filename that establishes:

• the date and time period covered,
• the epoch,
• the product version and any fixes that have been applied since the major version release.

This information is also contained in metadata within the file.

In general, users will want to find granules that have the latest available major revision number (currently this is R05), and also the latest fix (if any are present).

Information about versions and filenames can be found here.

Nearly all granule-level CloudSat data (Level 0 through 2C) are in HDF-EOS format.

Gridded Level 3 data are in netCDF version 4 format.

Level 2D data are produced by external organizations, and may be in a variety of formats.

We maintain a list of software tools that can be used to read CloudSat data.

CloudSat, which launched from Vandenberg Airforce Base on April 28, 2006, is the satellite platform carrying the Cloud Profiling Radar (CPR). The CPR is a 94 GHz (W-band) radar. Its relatively high frequency makes it sensitive to the presence of the droplets and ice crystals that form clouds, and it is the first spaceborne radar to make observations of this type. It also observes precipitation-sized particles, although the radar signal attenuates when precipitation is too heavy.

The radar has a ground footprint of about 1.5 km, and a vertical resolution of 240 m (oversampled). A new profile through the atmosphere is collected every 0.16 seconds.

CloudSat flies in a polar, sun-synchronous orbit, completing one revolution in approximately 99 min. This means there are about 14.6 complete revolutions around the Earth per day. Since the sampling interval is 0.16 seconds, the satellite moves 1.1 km relative to the Earth’s surface during this time.

Sun-synchronous means that the satellite always crosses the equator (from south to north) at the same local solar time, which is approximately 13:30 (1:30 in the afternoon). This time is referred to as the local time of the ascending node, or LTAN.

The data collected during one such revolution around the Earth is organized into one granule. The main CloudSat products (Level 2B and 2C) are produced as granules, so you get one orbit of information per file.

The ground track (you can view today’s here) repeats every 16 days. The following figure shows the ground track for one particular 24 hour period. Blue lines are ascending orbits, and red lines are descending. Note that the satellite would have likely passed over completely different points on Earth if a different random day was chosen, but the pattern shown would still be the same.

CloudSat has spent much of its life flying in formation with other satellites. During formation flying, the slice of atmosphere that the CPR views overlaps with the field of view of instruments on other satellites.

CloudSat has a particularly close relationship with partner satellite CALIPSO and its CALIOP lidar. The two satellites launched on the same rocket, and since they fly in formation, they can be used synergistically together to profile most hydrometeors in the Earth’s atmosphere. In particular, CALIOP views many of the tenuous cirrus clouds that are below CPR’s sensitivity, and CPR penetrates through deeper clouds where CALIOP loses signal.

CloudSat and CALIPSO flew in formation with the A-Train until February 2018. In October 2018 the two satellites rejoined to form the C-Train. For more information on important dates in the life of CloudSat, see the section “Important dates and things to keep in mind”.

The CloudSat help desk can be reached by filling out this form.

Some core references for CloudSat describing the mission and radar specifications:

• Stephens, G. L., and Coauthors, 2008: CloudSat mission: Performance and early science after the first year of operation. J. Geophys. Res., 113, D00A18, https://doi.org/10.1029/2008JD009982.
• Tanelli, S., S. L. Durden, E. Im, K. S. Pak, D. G. Reinke, P. Partain, J. M. Haynes, and R. T. Marchand, 2008: CloudSat’s cloud profiling radar after two years in orbit: Performance, calibration, and processing. IEEE Trans. Geosci. Remote Sens., 46, 3560–3573, https://doi.org/10.1109/TGRS.2008.2002030.

Core references for most CloudSat data products are listed on the page dedicated to that product. You can find these using the “Data Products” pulldown menu at the top of this page. We encourage users to tell us about publications they have submitted that use CloudSat data. The publications list can be found here.