IEEE Geoscience and Remote Sensing Magazine - December 2015 - 12

aggregations enable middleware (OPeNDAP) services to
access a single up-to-date reference point for access to an
entire time series of data granules for any specific location
or area of interest.
The combination of more robust hardware for accessing data archives and the expansion of web services to
enable access, have identified the need for an extra layer
of services to manage and orchestrate more basic data services. Although open-source
and widely accepted services
such as OPeNDAP can provide interactive access to LP
TO SiMPLiFY THe
DAAC data, these services
iNTerACTiON BeTweeN THe
often present interfaces in
uSer AND OPeNDAP, THe LP
raw service form, which can
be complicated to use and
DAAC HAS DeveLOPeD A
difficult to implement. AddweB ServiCe APPLiCATiON
ing higher level web services
PrOgrAMMiNg iNTerFACe.
that are capable of integrating these low-level services
together, simplifying them,
and expanding their usefulness will extend accessibility to non-scientist and general
public users, in addition to more knowledgeable scientists
desiring a more complex yet more direct user experience.
The resultant functionality of combined middleware services ties together the low-level services into "workflows",
enabling more useful processing and science application of
the requested data.
4. LP DAAC MiDDLewAre ServiCeS
Middleware can have many definitions based on the context of the implementation. For LP DAAC development,
middleware is a software layer between a client application
and the OPeNDAP data layer. This definition of middleware includes web servers, application servers, and a set of
software tools, scripts, and libraries bundled in a Software

Development Kit (SDK) that supports application development and data delivery. The middleware enables communication and management of data in a distributed application environment.
Middleware services help simplify OPeNDAP data
calls. HTTP requests to OPeNDAP for data retrieval are
complicated to compose manually. To formulate a request,
information about the desired product must be known.
Components of a request could include: geolocation; pixel
resolution; tiling scheme; compositing methods; acquisition timeline; etc. To simplify the interaction between the
user and OPeNDAP, the LP DAAC has developed a web
service Application Programming Interface (API). The API
interacts with the multiple services, which allows users
to take full advantage of OPeNDAP's benefits (e.g. data
sub-setting and temporal aggregation) without having to
assemble complicated OPeNDAP calls. Accessing these
services enables users to request spatial and temporal subsets of data without having to download and process entire data granules. This capability significantly reduces the
amount of data users must download for analysis and the
subsequent amount of time needed to extract the specific
information desired.
Figure 2 illustrates the conceptual design of LP DAAC
OPeNDAP and middleware services architecture, in which
multiple services can be chained together into "processing
work flows".
The hardware and software are configured to handle
the load-balancing of requests, and manage the low-level
access to the LP DAAC Data Pool and other EROS data resources. This architecture will accommodate users ranging
from the general public to the most technically astute. The
methodology makes it straightforward for most categories
of users to leverage the value of Earth science data acquired
by the Earth observing satellites archived at the LP DAAC.
Many users are seeking information and knowledge derived from LP DAAC data sets and may only be interested in

Firewall

Product Service
Web Service API

REST

Web Service Gateway Interface

Web Service Architecture

Sample Service
Task Service
Bundle Service
Quality Service

OPeNDAP
Cluster

LP DAAC
Data Pool

Web Service Clients
Figure 2. Middleware Service Layers Architecture for Access to LP DAAC Data Archives.

ieee Geoscience and remote sensing magazine

december 2015

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