[NCSA website](http://hdf.ncsa.uiuc.edu/) (<http://hdf.ncsa.uiuc.edu/>)
the homepage of NCSA, creator of HDF.

# HDF

**HDF file samples:**

-   DAAC, or [EOS
    Gateway](http://redhook.gsfc.nasa.gov/~imswww/hidden/imswelcome/)
    http://redhook.gsfc.nasa.gov/%7Eimswww/hidden/imswelcome/

-   FTP server (<ftp://modis.gsfc.nasa.gov/pub/Data_Sets/>) to get
    sampled EOS data.

**HDF-4** and previous versions are not compatible with HDF 5. They are
conceptually similar but HDF 5 is a new format and new library.

**HDF-4** can't go over 2GB and has 6 different data models for SD, GR,
RI, Vgroups, annotations, and Vdatas.

**HDF-5** allows for files over 2GB with unlimited number of objects. It
is one data model (multidimensional array of structures), with parallel
support.

**HDF-5** is much faster than HDF4 in I/O operations, especially as the
data size increases; then HDF-5 performs increasingly faster than HDF-4.

**HDF-4** is created from 1988 version of HDF. It has 6 basic objects:

-   Raster image

-   Scientific Data Set (SDS)

-   Vgroups

-   Vdata (tables)

-   Annotations

-   Palette

**HDF-5** is created using 2 objects:

-   Primary Objects

    -   **Datasets:** Multidimensional array of elements, together with
        supporting metadata

    -   **Groups:** Directory like structure containing groups,
        datasets, and other objects

-   Secondary Objects

    -   Dataspaces

    -   Datatypes

**HDF-5 Datasets Components**

-   **Array:** an ordered collection of identically typed data items
    distinguished by their indices (subscripts). This is similar to a
    spreadsheet of numbers.

-   **Dataspace:** Information about the size and space of a dataset
    array and selected parts of the array

-   **User-defined attribute list:** This defines what the data
    represents

-   **Special storage options:** extendable, chunked, compressed, and
    external

-   **Extendable**: Arrays can be extended in any direction

-   **Chunked**: Better sub-setting access time; extendable

-   **Compressed**: Improves storage efficiency, transmission speed

-   **External**: Metadata file in 1 file and raw data in another file.

# HDF links

[NCSA website](http://hdf.ncsa.uiuc.edu/) (<http://hdf.ncsa.uiuc.edu/>)
the homepage of NCSA, creator of HDF.

Some sample NCSA java tools for manipulating HDF
([http://hdf.ncsa.uiuc.edu/hdf-java-\
html/](http://hdf.ncsa.uiuc.edu/hdf-java-html/))

Software using HDF (<http://hdf.ncsa.uiuc.edu/tools.html>): On it
there's link to WebWind, IDL, and many more commercial and
non-commercial software for using HDF. There's a brief summary of each
program and what it does with HDF.

# HDF Visualization Tools

## IDL

It's commercialized software. It requires licensing to use it. It's a
command line-based program. It's an interpretive language. Similar to
MATLAB, IDL is design to work with arrays. The visualization suite on
IDL is amazing. It can put out pictures, graphs, histograms, charts,
tables, and you name it. It can create script, so the same command
doesn't have to be typed over and over again.

It has a steep learning curve, as the user must be familiar with all the
different commands and function that IDL has. However, there's a very
easy to use getting started guide, along with numerous other guides and
references that will help the user get started right away. The tech
support was very friendly. I was able to get clear help and my questions
were replied to speedily.

Converting HDF SD to image was hard at first, since the instruction
wasn't clear in the help menu, but with the help of the tech support, it
was finally accomplished in about 3 days of trying. There's 40 LUTs
(Look-Up Tables), which the user can select for non-indexed image. Some
of the LUT was not very good for the application, but since there are so
many LUTs, there's a couple that usually fits pretty well. If none of
the LUTs fit, there's also customable palette, which the user can
specific which pixel value represent what color. The power of IDL is
totally beyond WebWind.

To validate the software so that you have full access to IDL rather than
the \"time-out\" restrictions in Demo Mode, please be sure you have
properly installed the IDL software on your computer system. After the
software has been installed please refer to the evaluation instructions
on our web site at
<http://www.rsinc.com/license/windows/eval/index.asp>?

Windows Flexlm Evaluation Validation\
\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\
Product: IDL 5.5\
Expiration: 24-Aug-2002\
Key: 2EF0AB9AD21154EC-138\
\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*

## WebWind (HDF Visualization Tool)

A java program that can visualize HDF4 format files. It's not so
user-friendly, but it employs GUI (Graphic User Interface). The downside
to this program is that it's very obsolete GUI, and the tutorial or help
support were not very informative. For example, to get any kind of tech
support, there's a tech support fee required.

This java program is pretty demanding on the system. It takes a while to
do multiple operations. The display is pretty crude. It only can display
256 colors. It does, however, have the ability to change the palette so
that the user can define what color goes with what pixel value.

Downfall of this program is there's not really a good help guide to get
the user started. And there's no troubleshooting guide, so the user
cannot troubleshoot if the program doesn't function the way he wants it.
It's very quirky; sometimes the scripts that the website posts for
running demos do not even work as well. So that's another problem: the
program would not even run the supplied demo sometimes.

## Matlab (HDF Visualization Tool)

A mathematical program that specialize in handling arrays. It is use at
University of Michigan's Engineering Department. It is useful and like
IDL, it is an interpretive language. The program is similar to IDL in
most aspect. Didn't physically try out HDF with Matlab.

## Hoped for Functionality of an HDF Visualization Tool

This program would have an intuitive GUI. An online tutorial that would
walk the user through how to specifically access the HDF file, extract
only the data needed, and offer options on appropriate attributes (e.g.,
color range) for it. Also, the program would be fast (not java-based!).
The interface would be configurable, where it wouldn't prevent a user,
who really doesn't understand how HDF works, to extract the HDF data and
play with it.

The program would have many options of displaying the data from simply
displaying the image, overlaying it on a 3D globe, displaying it on a
line graph or scatter diagram, or showing it in a 3D model.

For example, in the EOS atmosphere HDF file. The program would represent
the cloud particle phase in 3D. The x and y axis would be the longitude
and latitude control respectfully, and the z-axis would be the altitude
of where the user is viewing the data. That way, the user can fly
through the atmosphere and watch how longitude, latitude, and altitude
would all effect cloud particle phase. IDL has very good representation
tools, and can visualize the data in 3D, but it lacks the
user-friendliness.

There should be a translator that would adjust the palette to the
attribute, without requiring the user to change the palette manually for
each data set displayed. However, the option to change the palette
manually should still be available.

# Level of Data Processing

NASA defines each level as the amount of processing a data set coming
off a satellite received. The lower the number the more raw the data set
is.

## Level 0

The data then undergo level zero processing (per NASA\'s standard
terminology) as soon as all the data contained within the current 24
hour time frame have been received. In level zero processing, duplicate
data are removed from the data stream, data are time ordered, and data
quality and accounting summaries are appended. The data are formatted
into a 24-hour **Science Routine Data Set File** (Level 0 data file).
Production of Level 0 data is now the responsibility of the ACE Science
Center at Caltech.

## Level 1

In level one processing, the data are separated out by instrument and
each instrument data set is formatted (using the [**NCSA
HDF**](http://www.srl.caltech.edu/ACE/ASC/hdf.html) standard) in a
fashion which is both consistent with the other instruments and
customized to meet the special requirements of that data set and team.
At this point in the processing, i.e., in level one, the data are
supplemented with ancillary data including position, attitude, and spin
phase of the spacecraft; command history and comments; calibration of
the spacecraft clock; and documentation of the data items. Excepting the
documentation, these ancillary data are all received by the Science
Center from the IMOC. The level one data are archived at the Science
Center and a copy is transmitted to the [**National Space Science Data
Center**](http://nssdc.gsfc.nasa.gov/) (the NSSDC) for long term
archiving. Each instrument team receives a copy of all the level one
data, including, of course, that from their own instrument

Processing of data beyond level 1 is carried out by individual
instrument team.

## Level 2

The processing at this stage is carried out by each individual
instrument team.

Data processing beyond Level 1 is the responsibility of the individual
instrument teams. Level 2 processing includes such operations as
application of calibration data and detector response maps, organization
of data into appropriate energy and time bins, and application of
ancillary data (for example, conversion of magnetic field vectors to
useful coordinate systems using the spacecraft attitude data). The
Science Center attempts to facilitate these efforts within its
resources, especially when high-level processing involves multiple
instrument teams. For example, much of the anisotropy/flow data for the
particle instruments, in particular for the Electron, Proton, and
Alpha-particle Monitor (EPAM), will be computed in terms of the
direction of the magnetic field. Thus the EPAM team will need high-level
results from the MAG team to do high level EPAM analysis. The Science
Center can facilitate data sharing and communications with its
substantial data storage capabilities and its data formatting
experience. Another example is the high level processing for the Cosmic
Ray Isotope Spectrometer, CRIS. Four institutions are involved in this
processing, each contributing expertise, and experience in a different
sub-assembly of this very complex instrument. Communications and
iteration of the data processing are being facilitated by the Science
Center for this team.

Each instrument team is required to deliver level two data back to the
Science Center, which will then make the data available to the other
instrument teams, the space science community (as required by NASA), and
the [**NSSDC**](http://nssdc.gsfc.nasa.gov/) for long term archiving.
Delivery of level two data back to the Science Center is expected to
begin about three months after the spacecraft enters orbit about the L1
Lagrangian point. Thereafter, roughly a two month lag time is expected
between receipt of level one data by the instrument teams and delivery
of level two data back to the Science Center. However, these delivery
schedules may require revision if instrument checkout and debugging take
longer than expected. In addition, the level two dataset is expected to
be evolutionary, in the sense that an instrument team may enhance their
level two data with additional products in the future, as the
sophistication of their analysis increases.

## Data Processing: Special Case for EOS

EOSDIS [**captures science data from all EOS
spacecraft**](http://esdis-it.gsfc.nasa.gov/add/edos.htm) and processes
them to remove telemetry errors, eliminate communication artifacts, and
create Level 0 Standard Data Products that are \"raw\" data as measured
by the instruments

All EOS instruments must have Level 1 Standard Data Products, most have
products at Level 2 and Level 3, and some have Level 4 Standard Data
Products. Some EOS Interdisciplinary Science Investigations also
generate Level 4 Standard Data Products. Specifications for the set of
standard data products to be generated are reviewed by the EOS IWG and
NASA Headquarters to ensure completeness and consistency in providing a
comprehensive science data output for the EOS mission. Standard data
products are produced at the DAACs or Science Investigator-led
Processing Systems (SIPSs).

EOS standard data products will be available at various product levels
ranging from Level 0 to Level 4. Level 0 data products are raw EOS
instrument data at full instrument resolution. At higher levels, raw
instrument data is converted into more usable parameters and formats
that are of interest to the Earth science community. At Level 4,
parameters are further refined through the use of models.

### Level 0 

Reconstructed, unprocessed instrument/payload data at full resolution;
any and all communications artifacts, e.g., synchronization frames,
communications headers, duplicate data removed. In most cases these data
are provided by EDOS to a DAAC as Production Data Sets for processing by
the SDPS in the DAAC or by the SIPS to produce the higher level
products.

### Level 1A 

Reconstructed, unprocessed instrument data at full resolution,
time-referenced, and annotated with ancillary information, including
radiometric and geometric calibration coefficients and georeferencing
parameters, e.g., platform ephemeris, computed and appended but not
applied to the Level 0 data.

### Level 1B 

Level 1A data that have been processed to sensor units (not all
instruments will have a Level 1B equivalent).

### Level 2 

Derived geophysical variables at the same resolution and location as the
Level 1 source data.

### Level 3 

Variables mapped on uniform space-time grid scales, usually with some
completeness and consistency.

### Level 4 

Model output or results from analyses of lower level data, e.g.,
variables derived from multiple measurements

# Metadata Available

**DIF** (Directory Interchange Format) Used by GCMD

**ISO 19115/TC 211 Geographic Information/Geomatics Metadata Standard**.
A developing Geospatial Standard that is being formulated by ISO. It is
currently an ongoing process.

**Documenting a data set from a satellite.**

DAAC submits DIF (Directory Interchange Format) to GCMD. It summarizes
geophysical parameters, spatial and temporal coverage, and other data
details. This documentation allows the data to be searchable under the
GCMD and EDG.

The DIF becomes metadata for the products. This metadata is submitted to
a master database, where it is used as metatag for online searching.
Therefore, making the data more accessible to users.

DAAC data set may include additional documents:

-   **User's guide** -- as the name implied

-   **Source Document** -- Describe how the data was collected and what
    collected it.

-   **Instrument Document** -- how the instrument collected the data

-   **Campaign Document** -- explains the details of which project
    funded this data collection

# NASA Earth Science Data from Satellites

-   EOS Spacecrafts in low-Earth orbit gather data from their
    instruments onboard.

    -   Examples of current EOS spacecrafts in orbit

        -   LANDSAT 7

            -   ETM+

                -   Terrestrial Surface

        -   Terra

            -   CERES

            -   MISR

            -   MODIS

            -   ASTER

            -   MOPITT

                -   Clouds, aerosols, and radiative balance

                -   Characterization of terrestrial surface

                -   Carbon cycle

    -   Different methods of remote sensing

        -   Passive Method

            -   Radiometer

            -   Imaging Radiometer

            -   Spectrometer

            -   Spectroradiometer

        -   Active Method

            -   Radar

            -   Scatterometer

            -   Lidar

            -   Laser Altimeter

    -   Missions is controlled by FOS

        -   Planning and coordinating missions

        -   Monitoring spacecrafts health

        -   Creating contingency plans

        -   FOS is at GSFC

        -   Instrument teams' facilities: Instrument Support Terminals

-   EOS spacecrafts send raw data and receive commands from ground
    stations

    -   White Sands Complex at White Sands, NM

    -   EOS Polar Ground Stations

        -   Svalbard, Norway

        -   Poker Flat, AK

    -   Ground stations send it to EDOS

-   EDOS receives raw data and generate Level 0 products

    -   Removes telemetry artifacts

    -   Creates sets of non-overlapping raw data

    -   Send data to appropriate DAACs

    -   Backup the Level 0 data.

-   DAACs

    -   8 DAAC around the nation

        -   JPL

            -   Jet Propulsion Lab

            -   Ocean Circulation and Air-Sea Interaction

        -   ASF

            -   Alaska SAR Facility

            -   Sea Ice and Polar Processes Imagery

        -   EDC

            -   EROS Data Center

            -   Land Processes Imagery

        -   ORNL

            -   Oak Ridge National Laboratory

            -   Ground-Based Data Relating to Biogeochemical Dynamics

        -   CIESIN

            -   Consortium For International Earth Science Information
                Network

            -   Socio-Economic Applications

        -   GSFC

            -   Goddard Space Flight Center

            -   Upper Atmosphere, Atmospheric Dynamics, and Global
                Biosphere

        -   LaRC

            -   Langley Research Center

            -   Radiation Budget, Aerosols, and Tropospheric Chemistry

        -   NSIDC

            -   National Snow and Ice Data Center

            -   Cryosphere (non- SAR)

    -   Supported by SDPS (provides hardware and software assistance)

        -   Product generation

            -   Generate products from Level 1 to Level 4

                -   Products must be at Level 1

                -   Most products at Level 2 or Level 3

                -   Products generated by SPDS

                    -   Provides software

        -   Data Archiving and Distributing

            -   EDG

                -   End users

                    -   Scientists

                    -   Educators

            -   Distributing data to SPIS for cost effective analysis

                -   Lead by Instrument Principal Investigator/Team
                    Leaders or Designees

                -   Gets Level 0 products from DAACs

                -   Produce higher Level products from Level 0 products

                -   Send the refined products back to DAACs for Storage
                    and Archive

        -   Information management

        -   User support

For reference to Acronyms and/or technical terms refer to documented
titled Acronyms & Glossary. For the detail explanations of different
Level of products refer to Level of Data Processing document.

# Acronyms & Glossary

**All EOS acronyms can be looked up on the web from** [ESDIS Acronyms
website](http://romulus.gsfc.nasa.gov/acronyms/acroFrameset.html)**.**

## Ancillary Data

Ancillary data is data provided by various sources in addition to what
is telemetered from the spacecraft. This includes [**attitude and
position solutions**](http://www.srl.caltech.edu/ACE/ASC/orbit.html)
from Flight Dynamics and [**onboard clock calibration
data**](http://www.srl.caltech.edu/ACE/ASC/clock.html) from the Flight
Operations team. These data are either folded into the Level 1 data at
the Science Center, and/or provided to the instrument teams in addition
to the Level 1 data.

## DAAC

The NASA [**Distributed Active Archive
Center**](http://nasadaacs.eos.nasa.gov/). They distribute data from
NASA's past and current data from research satellites and field
measurement programs. They catalog the data and "help make user easily
find the data they need easily." The DAAC are the operational data
management and user services arm of EOSDIS. Data from EOS and other NASA
Earth science missions are processed and stored at different DAACs. Each
DAAC is chosen for its expertise and capabilities to handle a specific
kind of data. DAAC is Type 1 ESIP. This means that they are the primary
distributors of satellites and ground based data sets. There are eight
DAACs chosen out of institution by NASA to provide processing,
archiving, and distributing data and provide user support.

## EDG

[**EOS Data
Gateway**](http://redhook.gsfc.nasa.gov/~imswww/pub/imswelcome/plain.html).
Multi-DAAC search gateway. Searching for data sets are done at each DAAC
center is not only limited to the resources stored at that DAAC center,
but also all the other DAAC as well as at other EOSDIS and international
data center. A web-based search engine. Provides numerous ways of
customizing the data selection from geographic regions to time range.
The search is free, but getting access is not. Like all other services,
gaining access to most Earth Science Data cost money.

## EDOS

**EOS Data and Operations System**. Captures high rate science and
engineering data from EOS spacecrafts and instruments, processes
telemetry to generate Level 0 products, and maintains a backup archive
of Level 0 Science Data Products. It removes telemetry artifacts,
creates sets of non-overlapping raw data as sensed by the individual
instruments over specific time intervals, and sends them to the
appropriate DAAC. In the case of a data loss at any of the DAACs, the
data can be recovered from the backup archive within EDOS. If the backup
Level 0 data within EDOS was lost, then the corresponding data can be
recovered from the appropriate DAAC. Level 0 are provided by EDOS to a
DAAC or a SIPS for product generation.

## EOSDIS

[**Earth Observing Science Data and Information
System**](http://eosdismain.gsfc.nasa.gov/eosinfo/EOSDIS_Site/). EOSDIS
manages data from NASA\'s Earth science research satellites and field
measurement programs, providing data archiving, distribution, and
information management services. Performs mission operations for
instrument and spacecraft control. Captures and process telemetry data.
Generates higher level standard data products. Archives and distributes
data products.

EOSDIS uses a distributed, open system architecture. This permits
allocation of EOSDIS elements to various locations to take best
advantage of different institutional capabilities and science expertise.
EOSDIS includes several major components - [Distributed Active Archive
Centers](http://romulus.gsfc.nasa.gov/eosinfo/EOSDIS_Site/Overview.html#daacs%23daacs)
(DAACs), [Science Data Processing
Segment](http://romulus.gsfc.nasa.gov/eosinfo/EOSDIS_Site/Overview.html#sdps%23sdps)
(SDPS), [Science Investigator-led Processing
Systems](http://romulus.gsfc.nasa.gov/eosinfo/EOSDIS_Site/Overview.html#sips%23sips)
(SIPSs),
[Networks](http://romulus.gsfc.nasa.gov/eosinfo/EOSDIS_Site/Overview.html#nets%23nets),
[EOS Data and Operations
System](http://romulus.gsfc.nasa.gov/eosinfo/EOSDIS_Site/Overview.html#edos%23edos)
(EDOS), and the [Flight Operations
Segment](http://romulus.gsfc.nasa.gov/eosinfo/EOSDIS_Site/Overview.html#fos%23fos)
(FOS)

## EOS

[**Earth Observing System**](http://eospso.gsfc.nasa.gov/). It has a
science component and a data system supporting a coordinated series of
polar-orbiting low inclination satellites for long-term global
observations of land surface, biosphere, solid Earth, atmosphere, and
oceans. It is the boss of EOSDIS.

## EOS Network

The network that allow user to access data sources. It moves Level 0
science data products from EOS Data and Operations System (EDOS) to the
DAACs.

## Ephemeris

A tabulated statement of the assigned places of celestial body for
regular intervals. Almanac showing daily positions of heavenly bodies

## ESDIS

[**Earth Science Data and Information
System**](http://eosdismain.gsfc.nasa.gov/eosinfo/ESDIS_Site/index.html).
Provide users access to data from NASA's Earth Science Enterprise.
Working to setup standards for scientific information exchange. To
develop interoperability functions with other data centers. To work
toward a Global Change Data and Information System. The ESDIS project
develops, implements, and operates the data and information system
called EOSDIS.

## ESE

The [**Earth Science Enterprise**](http://www.earth.nasa.gov/) has three
main components: a series of Earth-observing satellites, an advanced
data system, and teams of scientists who will study the data. It is one
of the main enterprise for NASA. It is the big boss of Earth Science.

## ESIP

[**Earth Science Information Partnership
Federation**](http://www.esipfed.org/). It's a group that brings
together government agencies, universities, non-profit organization, and
commercial businesses. It wishes to use all these resources to allow
Earth Science Information to be available to a broader community.
Currently, DAAC is part of this federation. It also has a website, where
the commercials businesses can sell their products, such as CD-ROM
online.

## EROS

[**Earth Resources Observation Systems**](http://edc.usgs.gov/). Data
management, systems development, and research field center for the US
Geological Survey's National Mapping Division.

## FOS

**Flight Operations Segment**. It is made up of the EOS operation center
at GSFC and instrument teams' facilities' Instrument Support Terminals.
They coordinate the mission planning; maintain the health of the
spacecraft. FOS develops contingency plans. FOS basically monitor the
flight operation of the spacecrafts and making sure that the spacecrafts
are doing what they are doing what they were designed to do.

**GCDIS**

[**Global Change Data and Information
System**](http://globalchange.gov/). EOSDIS is NASA's contribution to
this interagency. This organization facilitate the exchange of Earth
Science data internationally, so that international scientists can share
and discover how Earth is changing.

## GCMD

[**Global Change Master Directory**](http://gcmd.gsfc.nasa.gov/). Uses
DIF (Directory Interchange Format). Includes data sets covering: climate
changes, biosphere, hydrosphere and oceans, geology, geography, and
human dimensions of global change. The public may search the database
for the type of data sets they are looking for free of charge. The
database will tell you the location of the data sets.

## HDF

**Hierarchical Data Format**. It is a file format being used by many
different agencies and research groups. It allows for multi-object files
to be shared easily. It was created by
[NCSA](http://hdf.ncsa.uiuc.edu/). Types of data supported.

-   Scientific Data sets \-- Multi-dimensional integer or floating point
    arrays

-   Vertex Data (Vdata and Vgroups) \-- Multi-variate data stored as
    records in a table

-   General Raster (GR) \-- Raster images

-   Annotation \-- Text strings to describe files and parts of files
    (metadata)

-   8-bit Raster images

-   24-bit Raster images

-   Palette \-- 8-bit color palettes (accompany images)

## Metadata

Descriptive information that characterizes a set of quantitative and/or
qualitative measurements and distinguishes that set from other similar
measurement sets. These attributes help the user determine if the data
set is useful to their needs.

## Raster

A scanning pattern of parallel lines that form the display of an image
projected on a cathode-ray tube of a television set or display screen.

## Raster Images

General Raster, or GR, data model can store 8-bit or 24- bit raster
image. Raster image is a 2D array. CLUT (color look up table),
compression method, and attributes can be attached to GR.

## Remote Sensing Methods

### Passive Methods

Instrument that doesn't supply its own detection power, but rather picks
up natural energy. It only senses the radiation emitted by the object
being viewed.

### Radiometer

An instrument that quantitatively measures the intensity of
electromagnetic radiation in some band of wavelengths in the spectrum.
Usually a radiometer is further identified by the portion of the
spectrum it covers; for example, visible, infrared, or microwave.

### Imaging Radiometer

A radiometer that includes a scanning capability to provide a
two-dimensional array of pixels from which an image may be produced is
called an imaging radiometer. Scanning can be performed mechanically or
electronically by using an array of detectors.

### Spectrometer

A device designed to detect, measure, and analyze the spectral content
of the incident electromagnetic radiation is called a spectrometer.
Conventional, imaging spectrometers use gratings or prisms to disperse
the radiation for spectral discrimination.

### Spectroradiometer

A radiometer that can measure the intensity of radiation in multiple
wavelength bands (i.e., multispectral). Oftentimes the bands are of a
high spectral resolution---designed for the remote sensing of specific
parameters such as sea surface temperature, cloud characteristics, ocean
color, vegetation, trace chemical species in the atmosphere, etc.

### Active Methods

Provides its own energy to illuminate the object. It takes data on the
reflected radiation or backscattered from the particular object.

### Radar (Radio Detection and Ranging)

A radar uses a transmitter operating at either radio or microwave
frequencies to emit electromagnetic radiation and a directional antenna
or receiver to measure the time of arrival of reflected or backscattered
pulses of radiation from distant objects. Distance to the object can be
determined since electromagnetic radiation propagates at the speed of
light.

### Scatterometer

A scatterometer is a high frequency microwave radar designed
specifically to measure backscattered radiation. Over ocean surfaces,
measurements of backscattered radiation in the microwave spectral region
can be used to derive maps of surface wind speed and direction.

### Lidar (Light Detection and Ranging)

A lidar uses a laser (light amplification by stimulated emission of
radiation) to transmit a light pulse and a receiver with sensitive
detectors to measure the backscattered or reflected light. Distance to
the object is determined by recording the time between the transmitted
and backscattered pulses and using the speed of light to calculate the
distance traveled. Lidars can determine atmospheric profiles of
aerosols, clouds, and other constituents of the atmosphere.

### Laser Altimeter

A laser altimeter uses a lidar (see above) to measure the height of the
instrument platform above the surface. By independently knowing the
height of the platform with respect to the mean Earth\'s surface, the
topography of the underlying surface can be determined.

## Scientific Data Set

SDS has 4 primary data objects: arrays, dimensions, dimension scales,
and dimension attributes. SDS array is the fundamental object, while the
other 3 objects describe the array. The data is converted to an 8-bit
image using a standard algorithm.

## SDPS

**Science Data Processing Segment**. SDPS support product generation
(all the different level of processing), data archiving and
distribution, and information management. SDPS hardware and software
reside and operate at the DAACs. The software is used as product
generation algorithms. It helps the different centers to absorb and
store the data sets and make sure there's a standard for the products
they generated. It helps SIPS generate SDP (Standard Data Product) by
allowing SIPS to retrieve level 0 products and providing user access to
SIPS generated higher-level products through EOS Data Gateway. They also
provide software toolkits to assist instrument teams in their
development of product generation software. They are at DAACs.

## SIPS

**Science Investigator-led Processing Systems**. These facilities are
not at DAACs. They however still product EOS standard products. They are
under control of Instrument Principal Investigators/ Team Leaders or
their designees. They produced SDP based on cost-benefit analyses.
Products produced by SIPS using investigator-provided systems and
software are sent to appropriate DAACs for archival and distribution.
They begin the processing sequence by retrieving Level 0 data and
ancillary data from DAACs.

## Vdatas or Tables

A collection of records whose values are stored in fixed-length fields.
Therefore, the table is where each row has the same structure and each
column contains the same data type.

## Vgroups

A structure designed to associate related objects. Directories. Folders.