CERES Frequently Asked Questions

General Questions and Answers

What is CERES?

The Clouds and the Earth's Radiant Energy System (CERES) experiment provides radiometric measurements of the Earth's atmosphere from three broadband channels and is a follow-on to the Earth Radiation Budget Experiment (ERBE) mission. CERES products include both solar-reflected and Earth-emitted radiation from the top of the atmosphere to the Earth's surface. The CERES experiment will lead to a better understanding of the role of clouds and the energy cycle in global climate change.

Which spacecraft and instruments are used?

Instruments	Launch Dates
PFM	November 27, 1997 as part of the Tropical Rainfall Measuring Mission (TRMM) and was the first CERES instrument.
FM1 & FM2	December 18, 1999 into polar orbit on board the EOS flagship Terra.
FM3 & FM4	May 4, 2002 on board EOS Aqua.
FM5	October 28, 2011 on board Suomi National Polar-orbiting Partnership (NPP) satellite.
	Access CERES Instrument specifications and Operation scan modes by month.

What is TOA?

Top-of-the-Atmosphere (TOA) is a surface approximately 20 km above the Earth's surface.
The TOA is an ellipsoid x²/a² + y²/a² + z²/b² = 1
where a = 6408.1370 km and b = 6386.6517 km.

What is Flux?

Flux - is an energy flow through a unit area over a unit time; hence the units of W m-2. As radiation interacts with matter at all atmospheric layers and surfaces, measuring, understanding, and modelng the spatial, temporal and spectral distribution of fluxes is important. Flux characterizes our climate and is represented as Up, Down, Net, TOA & Surface.

What are Up, Down and Net Fluxes?

Given the vertical layered structure of Earth atmosphere above underlying surfaces, the vertical variability of these fluxes is of particular interest. Hence the term "Up" and "Down" for characterizing the direction of flow of radiative fluxes at a particular level. Moreover, by counting in or out these "Up" and "Down" energy fluxes, one can define a "Net" flux that is ultimately responsible for the net energy loss or gain within any two such layers. This concept is important in defining the radiative heating or cooling of each atmospheric/surface element.

What are TOA and Surface Fluxes?

The-Top-of-Atmosphere (TOA) layers are where the first interaction occurs as the radiation from the Sun reaches Earth and then the various atmospheric layers containing gases, clouds, aerosols, and/or other constituents before finally reaching the Surface. Solar radiation is scattered and/or absorbed in each of these material layers while the atmospheric and surface constituents emit their own share of radiation. Shortwave (SW) and Longwave (LW) are the two primary spectral parts the energetics can be split into and may be further divided into finer spectral intervals depending on the specifics of the physical processes under investigation.

What is the spectral range of the 3 CERES detectors?

Total	0.3 - 100.0 microns
Shortwave	0.3 - 5.0 microns
Longwave	8.0 - 12.0 microns

What is the equator crossing time of the CERES satellites?

Aqua has a 1:30 PM equator crossing time.
Terra has a 10:30 AM equator crossing time.

What is the CERES FOV or Footprint?

The CERES Field of View (FOV) is synonymous with the term Footprint and is determined by the Point Spread Function (PSF) which is a two-dimensional, bell-shaped function that defines the CERES instrument response to the viewed radiation field. The resolution of the CERES radiometers is usually referenced to the optical FOV which is 1.3° in the along-track direction and 2.6° in the cross-track direction. The CERES FOV or footprint size is referenced to an oval area that represents approximately 95% of the PSF response. Since the PSF is defined in angular space at the instrument, the CERES FOV is a constant in angular space, but grows in surface area from a minimum at nadir to a larger area at shallow viewing angles.

What is All-Sky and Clear-Sky?

All-Sky scene, also known as total, is determined from all CERES footprints (20 km nominal resolution) within the given temporal or spatial domain.

Clear-Sky scene, has different algorithms depending on the product ERBE-like, Single Scanner Footprint TOA/Surface Fluxes and Clouds (SSF), or Energy Balanced and Filled (EBAF). ERBE-like clear-sky scene is determined from CERES footprints that were crudely identified as clear using the ERBE scene id algorithm which uses climatological, zonal LW thresholds and appropriate SW thresholds based on 12 scene ids.

EBAF & SSF clear-sky scenes are determined from CERES footprints that are 99% clear as identified by CERES-MODIS clear-sky mask from the MODIS pixels contained within the CERES footprint. SSF clear-sky products contain many cloudy regions that may have no clear-sky observations for one particular month with no attempts to fill these regions. The EBAF clear-sky products filled all non-observed clear-sky regional fluxes for a complete clear-sky global map, and all temporal and spatial domains should have clear-sky fluxes.

Which modes do CERES Instruments operate in?

The Terra and Aqua satellites carry two CERES intruments onboard, one in Cross-Track mode and the other in Rotating Azimuth Plane Scan (RAPS) mode or in Fixed Azimuth Plane Scan (FAPS) mode. The first CERES instrument PFM, launched in November 1997 as part of the TRMM mission, was powered off May 29, 2001.

What are Cross-Track, Fixed and Rotating Azimuth Plane Scan modes?

Aqua and Terra satellites both carry two CERES instruments onboard that all CERES instruments are capabile of operating in. Fixed Azimuth Plane Scanning (FAPS) has scan lines perpendicular to the path of the satellite, while Rotating Azimuth Plane Scan (RAPS) lines are at a wide range of angles with respect to the satellite's path. An instrument operating in RAPS has increased spectral darkening of the transmissive optics. The Cross-Track instrument is recommended by CERES, since the spatial distribution of footprints is uniform.

What is the spatial coverage and temporal range?

CERES is a global data set whose satellite orbit determines the spatial coverage at the surface.

Satellites	Instruments	MinLat	MaxLat	MinLon	MaxLon	Spatial Altitude	Temporal Range
Aqua	FM3 & FM4	-90	90	-180	180	705 km	Jun 2002 - present
Terra	FM1 & FM2	-90	90	-180	180	705 km	Feb 2000 - present
TRMM	PFM	-40	40	-180	180	350 km	Dec 1997 - Sep 1, 1998 *occassional coverage for coincident overflights with Terra in 1999 - 2001

What are the CERES data types and default values?

1 byte integer	127
2 byte integer	32767
4 byte integer	2147483647
4 byte real	3.402823E+38
8 byte real	1.7976931E+38

What are the CERES data scene types?

Surf Index CERES Surface Type 1 Evergreen Needle Forest 2 Evergreen Broadleaf Forest 3 Deciduous Needle Forest 4 Deciduous Broadleaf Forest 5 Mixed Forest 6 Closed Shrubs 7 Open Shrubs 8 Woody Savannas 9 Savannas 10 Grassland

Surf Index CERES Surface Type 11 Wetlands 12 Crops 13 Urban 14 Crop/Mosaic 15 Permanent Snow/Ice 16 Barren Desert 17 Water 18 Tundra 19 Land Snow 20 Sea Ice

What are the associated parameters and temporal coverage?

Access the temporal coverage of available data sets by selecting each individual product.

Products	Select Parameters
BDS	Filtered Radiances, Detector Values, Instr. Engineering Parameters
CERES-NEWS	TOA Flux, Surface (Radiative) Flux, OLR, Surface Types, Aerosol Optical Thickness, Cloud Base Height, Cloud Top Height, Cloud Optical Depth, Aerosol Extinction Coefficient, Aerosol Base Height, Aerosol Top Height, Cloud Extinction Coefficient, Cloud Vertical Profile, Radar-only Liquid Water Content, Radar-only Liquid Ice Content, Vertical Flux Profile, Unfiltered Radiances, Filtered Radiances.
CRS	Cloud Properties, TOA Fluxes, Surface (Radiative) Fluxes, Unfiltered Radiances, Surface Types
EBAF	Clear-sky and All-sky TOA Adjusted Fluxes
ES-4	Clear-sky and Total-sky Fluxes, Clear-sky and Total-sky Solar Incidence, Clear-sky and Total-sky Albedo
ES-8	TOA Fluxes, Unfiltered Radiances, Filtered Radiances, OLR, ERBE Scene Identification
ES-9	Clear-sky and Total-sky Fluxes, Clear-sky and Total-sky Solar Incidence, Clear-sky and Total-sky Albedo
FSW	Clear-sky and All-sky TOA Fluxes, Surface (Radiative) Fluxes, OLR, Clear-sky and All-sky Albedo, Cloud Properties, Surface Types
ISCCP-D2like	Cloud fraction, Effective Pressure, Temperature, optical depth, IWP/LWP, particle size, IR Emissivity in PC/Tau bins similar to ISCCP-D2 product
SFC	Clear-sky and All-sky TOA Fluxes, Surface (Radiative) Fluxes, OLR, Clear-sky and All-sky Albedo, Cloud Properties, Surface Types
SRBAVG	Clear-sky and All-sky TOA Fluxes, Surface (Radiative) Fluxes, OLR, Clear-sky and All-sky Albedo, Cloud Properties, Surface TypesList
SSF	Cloud Properties, TOA Fluxes, Surface (Radiative) Fluxes, Unfiltered Radiances, Filtered Radiances, OLR, Surface Types
SSF/SYN1deg-lite	Cloud Properties, TOA Fluxes, Surface (Radiative) Fluxes
SYN/AVG/ZAVG	Clear-sky and All-sky TOA Fluxes, Surface (Radiative) Fluxes, OLR, Clear-sky and All-sky Albedo, Cloud Properties, Surface Types, Radiative Flux Profiles

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Data Products Questions and Answers

What CERES Data Products are available?

• Clouds and Computed Flux Profile Data Sets represent surface, within-atmosphere, and Top-of-Atmosphere (TOA) fluxes from radiative transfer model calculations with inputs from several sources.
• Clouds and TOA/SFC Flux Data Sets represents TOA and surface radiation derived from CERES and imager measurements.
• ERBE-like Data Sets are consistent with earlier ERBE processing.
• CERES-NEWS data integrates measurements from CERES, MODIS, CALIPSO, and CloudSat.
• CERES-MISR-MODIS (SSF-SSFM) data integrates measurements from CERES, MISR, and MODIS.
• Instrument data (BDS) represent Instrument Data.
• SSF/SYN1deg-lite Data Sets represent Single Scanner Satellite Footprint (SSF), Synoptic Radiative Fluxes (SYN), clouds, TOA and surface fluxes with improved CERES instrument Edition 3 (2010) calibration, processed with Edition 2 algorithms.

What do the CERES Product Levels represent?

Level	Processing	Products
Level 1B	Processed to sensor units	BDS
Level 2	Derived geophysical variables at the CERES footprint resolution as the Level1B source data	CRS, ES-8, SSF
Level 3	Radiative fluxes and cloud properties spatially averaged into uniform regional and zonal grids, globally and temporally averaged into daily, monthly hourly, or monthly means	AVG, ZAVG, ES-4, ES-9, FSW, ISCCP-D2like, SFC, SRBAVG, SYN, SSF/SYN1deg-lite
Level 4	Level3 products adjusted within their range of uncertainty to satisfy known constraints on the climate system	EBAF
	Access additional details on the CERES Processing Levels page.

Which products are available for subsetting?

Subsetting allows users to create smaller files (subsets) of the original data by selecting desired parameters, parameter criterion, or latitude and longitude coordinates.

• Energy Balanced and Filled (EBAF) Level 4 data sets with monthly and climatological regional, zonal, global averages of TOA clear-sky and all-sky LW and SW fluxes, where the net flux is constrained to the global heat storage in netCDF format.
• Single Scanner Footprint TOA/Surface Fluxes and Clouds (SSF) Level 2 data sets that are one hour of instantaneous CERES data for a single scanner instrument in HDF format.
• Single Scanner Satellite Footprint, TOA, Surface Fluxes and Clouds (SSF1deg-lite) Level 3 10 year data sets with a reduced parameter list of monthly and daily data in netCDF format.
• Synoptic Radiative Fluxes and Clouds (SYN1deg-lite) Level 3 10 year data sets with a reduced parameter list of monthly and daily data in netCDF format.

Order CERES Level 3 Edition 2.5 "lite" subset data from the CERES Level 3 Ordering Page.

Explain the CERES file naming convention

CERES file names are formed using the dataset name, configuration code and date information which make each file name unique.

A Dataset name consists of CER_<ProductID>_<Sampling-Strategy>_<Production-Strategy>
Eg. CER_SSF_Terra-FM1-MODIS_Edition2B

The SSF Filename consists of the <Dataset name> combined with the <Configuration Code> and <Date> to make it unique
Eg. CER_SSF_Terra-FM1-MODIS_Edition2B_120145.2001052812

<ProductID> Identification value - CRS, ES8, SSF, SYN
<Sampling-Strategy> Satellite, instrument, and imager - TRMM-PFM-VIRS, Terra-FM1-MODIS, Aqua-FM3-MODIS
<Production-Strategy> Edition or campaign - At-launch, Edition2, ValidationR1
<Config-Code> 6-digit file and software version management code number - 120145
<Date> Date in the form YYYYMMDDHH - 200105812 (May 28, 2001 GMT hr12)

How are the CERES products processed?

The CERES Processing and Data Flow Diagram shows the four levels of processing and the resulting products produced from various inputs provided. Clicking on individual products (represented in rectangles) displays additional information such as spatial and temporal coverage, file size and frequency, and data sets available for ordering.

Which CERES product should I use?

Products	Usage Suggestions
CRS	Consistent flux and cloud properties.
EBAF	Best estimate (net-balanced) TOA fluxes. Evaluation of climate model and energy budget.
ERBE-like	Compares original ERBE(1985 - 1989) fluxes with CERES. No CERES algorithm improvements.
FLASHFLUX	Quicklook near real-time.
ISCCP-D2like	Monthly cloud properties in a similar format to ISCCP.
SSF	Instantaneous footprint radiances, fluxes and MODIS clouds. TOA fluxes and clouds to compare with A-train (Aqua) products. TOA fluxes for long term climate trend evaluation, use SSF with associated cloud and aerosol properties.
SSF/SYN1deg-lite	10 year dataset (2000 - 2010) with an abbreviated parameter list and the latest CERES instrument calibration.
SYN	Best estimate surface fluxes. Instantaneous footprint level.

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Data Access Questions and Answers

How do I obtain CERES data?

• Order online ASDC Web Ordering Tool data available for ftp download.
• Order online CERES Subsetter Ordering Page data available for ftp download.
• Order online Reverb Search Tool data available for ftp download.
• Obtain the CERES CD Sampler a 5-volume CD set.
• Download the Readme and UNIX C shell script to extract regional CERES non-geo fluxes from the CERES SRBAVG1 HDF file.

What software tools can I use to view CERES HDF data products?

Visualize CERES data with view_hdf:

• view_hdf a visualization and analysis tool for accessing data stored in Hierarchical Data Format (HDF) and HDF-EOS.

What software tools can I use for CERES NetCDF data products?

• NetCDF is a set of software libraries and machine-independent data formats that support the creation, access, and sharing of array-oriented scientific data.

Is subsetting available?

Subsetting is available with one of the CERES Level 3 data products:

• Synoptic Radiative Fluxes and Clouds (SYN1deg-lite)

Order CERES Level 3 Edition 2.5 "lite" subset data from the CERES Level 3 Subsetter Page.
Order CERES Level 2 subset data via CERES Data and Information.