IEEE Geoscience and Remote Sensing Magazine - December 2015 - 13

interacting with high-level, web-based user interfaces. The
applications will gather input criteria from users, facilitate
the data request service calls, and finally notify users when
the data request has been completed. The users will be presented with a suite of interactive charts and graphs to assist
analysis. For this level of user, the application pages will
utilize service layer endpoints to power the applications behind the scenes, without direction from the user.
More sophisticated users may be looking for information derived from the foundational data. Users in this tier
want to know specifics about the measurements of the
data, though perhaps less about its structure and arrangement. The service layer endpoints will deliver information
that has been processed, analyzed, formatted, and structured in ways specified by the users through the higher
level service layers. This category of users may want to
know scripting, programming, and web service interaction details. These services have been designed to be simple to consume and require less low-level interaction to
return information.
The most sophisticated users may be comfortable
working directly with low-level OPeNDAP services. Users can formulate their own complex URLs to retrieve
and format data from OPeNDAP for their analysis of the
data and science application. Using these lowlevel services requires
knowledge of scripting,
programming,
HTML
request formatting and
execution, and the valid
data definitions and values. Service layer interfaces have been enabled
to allow automated machine-to-machine interaction for dynamically
delivering and formatting data to customized
user requests.
4.1. Consuming
serviCes using opensourCe Language
appLiCations
The middleware services
are configured to allow
users to interact with
them by making use of
a Representational State
Transfer (REST) architecture and the HTTP
protocol for communication. REST services, which
are an industry standard
technique, are flexible to
december 2015

implement and can be consumed with simple tools. Any
tools interacting with HTTP, such as web browsers, cURL,
and Wget, are also suitable for calling REST services. In addition, most modern programming languages provide modules for composing HTTP calls, making it straightforward to
incorporate calls to REST services into an application.
As with any HTTP call, the middleware services require
the caller to provide the appropriate URL and the list of parameters detailing the specific request (e.g. products and
date ranges). The middleware
services can also accept a parameter describing the data
format of the response, such
LP DAAC MiDDLeWAre
as JavaScript Object Notation
SerViCeS CAN Be
(JSON) or Comma-Separated
CONSuMeD uSiNg A SiMPLe
Values (CSV).
HTTP geT reQueST.
Additional processing and
software tools are required
to format and package the
requested products in a manner more user friendly than the raw OPeNDAP results.
These necessary middleware services conveniently operate between client applications and the data layer. Connections to an OPeNDAP cluster for data retrieval can be

Figure 3. Example Service Call to List Available Terra MODIS (MOD) Products.

Figure 4. Example Service Call to Obtain Information for a Product of Interest (e.g., MOD13A1 Version 005).

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Table of Contents for the Digital Edition of IEEE Geoscience and Remote Sensing Magazine - December 2015