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VI. INFORMATION SYSTEMS TECHNOLOGY
Over the past quarter century, OSSA has employed a mission-oriented
approach to the collection of data in support of a variety of science
applications. During each mission, data were collected to meet the
requirements of a small group of scientists in a particular discipline,
using a data system that had been developed for that purpose. However, as
noted earlier, there is an increasing need for interdisciplinary and multi-
discip~inary scientific work that will change the way information systems
are structured. OSSA knows that as it moves into the Space Station era
mission and discipline boundaries wild blur, and huge volumes of data will
be collected by NASA and others to support a large number of interdisci-
plinary projects involving hundreds of scientists. OSSA has already
initiated comprehensive planning for such missions and for the challenge
of information systems that can handle the huge volumes of data and the
product requirements of the users.
As an example, the Committee is concerned that even with efficient
data-rate management and control, the current digital magnetic recording
and compact disk (CD) read-on~y memory (ROM) technologies cannot cope with
anticipated data rates in the Space Station era. Further, commercial
database management systems currently do not have the features required to
manage large volumes of space-derived data. These technological problems
are compounded by such management and operational considerations as the
need to control costs (which potentially affects OSSA's ability to support
the users) and the need to support the users (which influences costs).
Therefore, the Committee suggests the following as the final major issue
to be addressed by OSSA in the context of this study:
Issue #4: How can the projected information systems technologies keep
pace with future sensor outputs?
After reviewing the technology requirements of NASA information sys-
tems in the Space Station era, the Committee believes the specific areas
of technological concern are:
41
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the trend toward development of higher data-rate instruments for
use in remote Earth sensing, taking into consideration the actual
user need and constraints imposed by information systems techno1-
ogy and costs (discussed below);
the ability of current digital magnetic recording and compact disk
(CD) read-only memory (ROM) technologies to cope with anticipated
data rates in the Space Station era in support of on-board process-
ing, space-to-ground transmission, "1eve1-zero" processing (that
is, data that have been corrected for telemetry errors and decom-
mutated), and the storage and retrieval of data (discussed below);
the ability of commercial database management systems to manage
large volumes of space-derived data (discussed below);
the need for cohesive planning and a unified approach to the
creation and control of software (discussed in Section Ill of this
report); and
the fragmented and mostly incompatible data transfer and
electronic communication between elements of the OSSA and the user
community, which makes data and information transfer difficult
(discussed in Chapter IV).
The Trend Toward ~ .
Scie ~ much data they can effec-
tive~y evaluate. Most users will want data over a small test site or a
sampling of the data to meet their scientific needs. The Committee does
not believe information systems should be designed to provide all data
acquired by the high data-rate instruments, unless there is an overwhe~m-
ing scientific justification. A careful cost-to-benefit analysis should
be made before designing a data system for the high-data-rate instruments.
Some data sensors have the capability of drowning data systems with so
much data that costs become unreasonable and technology may not even be
able to cope with the data stream. If all data is saved, one cannot
afford to extract the information that is really needed. Several sensors
such as the HIRIS and the synthetic aperture radar (SAR) that will be part
of EOS dominate the planned data volume environment. Technology improve-
ments should enable NASA to increase the cost effectiveness of handling
new data by a factor of ten by 1995. However, it appears that data gath-
ering may increase by much more than the technology gain unless careful
plans are made for use of the high-rate sensors.
The data rates for SAR tabout 300 megabits per second (Mbps)] and
HIRIS (up to 900 Mbps) compare with data rates to good computer disks of
24 Mbps, and Cray supercomputer specia1-channe] speeds of i,OOO Mbps.
With data rates even a fraction of these, one must establish a mechanism
to cope with questions of what sampling and data archiving make sense.
The strategy should include a projection of year-1995 technology and
costs, and an effort to drive data storage costs down. With lower storage
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costs, it is reasonable to save more data that will be used for local
studies and case studies for short time periods. Table ~ and Figure 4
summarize data rates from selected instruments during the next 10 to 15
years (also see Table 2 and Figures 5 through 7 at the end of this
chapter).
Another class of studies of growing importance requires processing
data over a number of years. If all OSSA does is to save high-volume data
for many years, it still cannot be used for such studies because it costs
too much. Often data need to be sampled in several ways, such as the one-
kilometer (high resolution) and four-kilometer resolution (global survey)
data that is routinely supplied to NOAA.
A common satellite data rate of 100 ki~obits per second (kbps) pro-
duces 3,160 x 109 bits per year, or 3,160 high-density tapes [6,250 bits
per inch (BPI)] each year. An individual PI usually can cope with only 20
to 100 tapes per year. A data center usually charges $60 to $100 per tape
copy, and then it often costs the PI even more to process it. The
International Satellite Cloud Climate Programme is now sampling data from
several geosynchronous-orbit satellites and one polar-orbiting satellite
to reduce the archive from about 60 x 1012 bits per year to two archives,
one of about 500 tapes (500 x 109 bits per year) and the other of about
100 tapes per year. The international processing unit at the Goddard
Institute for Space Studies is able to process the smaller of these two
archives to derive cloud statistics.
While the above data rate of 60 x 1012 bits per year has posed a
difficult problem for long-term studies, it should be noted that the
composite data rate being planned by NASA for 1995 is more than 50 times
greater (see Figure 7~.
In EOS, a NASA division proposed to limit the onboard system to hand
aggregate instrument rates not over 20 Mbps. The limit is under debate.
Other very-high-rate sensors such as SAR and HIRIS wild be handled sepa-
rately. The Committee thinks this NASA strategy is wise. The high data
rates demand more careful attention to decide what sampling strategies and
data rates make sense. The main uses for SAR are ocean wave statistics,
ice coverage and location, and J and resource studies. To obtain ocean
waves, one needs only a small, square array of samples located 100 or 200
km apart from each other, perhaps closer together in coastal waters or
near a major storm. As indicated above, it seems likely that user
requests for HIRIS channels will be rather modest compared with the capa-
biJity now being planned. The HIRIS instrument has similarities to instru-
ments on Landsat and the European SPOT. Comparisons should be made with
the data rates, duty cycle, archive strategies, and costs of these older
systems, as part of the process of defining the data system for HIRIS.
In forming sensing requirements, it would be helpful if OSSA would
provide feed-back to the users on the costs for different options in order
to arrive at a good balance of costs and benefits. also, the plans for
future data rates and archives should factor in better technology. It is
43
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le
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anticipated that there will be an increase in storage cost effectiveness
and of computing capability (per-unit cost) by a factor of 10 or 15 by
1995. However, one cannot plan for 100 times more archiving by 1995--when
technology is projected to be perhaps only 10 times better--without
carefully evaluating costs and benefits.
Since the Committee did not have the time to study this matter in
great detail it can do no more than suggest that it be given careful
review. In particular, the Committee is concerned that the likely budget
cuts in the foreseeable future will mean that increased funds for sophis-
ticated, and therefore expensive, information systems will come at the
expense of investigator, instrument, and spacecraft portions of the pro-
grams. When data requirements are being discussed, there will always be
some good reasons for better space resolution, more samples in time, and
more channels. However, users do not need the highest-resolution data al]
of the time. We believe that achieving a balance between data and infor-
mation systems and other aspects of the programs is essential.
Limitations of Current Digital Magnetic Recording and Compact Disk
.
(CD) Read-On~y Memory (ROM) Technologies. Even with efficient data-rate
management and control, the current digital magnetic recording and CD-ROM
technologies cannot cope with anticipated data rates in the Space Station
era. OSSA needs to examine and support, to at least a limited extent, the
development of alternate storage technologies, to support high throughput
rates and capacities. Hybrid analog and digital recording formats and
optical video disks similar to laser-vision disks are examples of a~ter-
nate technologies that can be exploited.
A careful examination of continuous-throughput data-rate requirements
for high-data-rate sensors is needed to reduce data volumes to a manage-
ab~e level that is both consistent with user requirements and affordable.
OSSA, in conjunction with the user community, should develop techniques
(including data compression and on-board data extraction techniques) to
reduce the data throughput requirements to a J eve] consistent with
contemporary technologies that are commercially available or expected to
be developed commercially in the near term.
In reviewing the requirements of the first three technologies listed
on the proceeding page, the Committee adopted the assumption that contin-
uous throughput requirements will vary from lob to lO9 bits per second
(bps) in the 1990 time frame (see Figures ~ through 7 and Table 2 at the
end of this section). The focus is on continuous rather than burst data
rates, since the tote] cost and complexity of the information systems will
to a large extent be determined by the continuous throughput
requirements. For data rates up to lob bps, technology currently exists
for space-to-ground transmission, and for processing, storing, and
distributing data electronically to most users. At this rate, data can be
processed ([eve] zero), archived using magnetic media, and distributed to
users in read time using commercial transmission facilities. OSSA
missions with non-imaging sensors or low-resolution imaging devices have
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continuous throughout rates of the order of 106 bps. These missions
generate up to 1o1 bits per year, and the data can be stored in about
10~000 physical storage units (PSU) such as tapes' disk packs' etc.
Input/output (I/O) rates of 100 bps are easily available with tape and
disk drives, and communications links operating at 1.544 Mbps (commonly
called "T1" links or carriers, in reference to their commercial tariff
designation) can be established easily at user locations for data
distribution. Processing speeds of 10 million instructions per second
(MIPS), or up to 100 instructions per byte of data, will be needed for
level-zero processing. Such speeds are currently available.
Increasing the throughput requirements to 107 bps will stretch the
current capabilities in some areas. One exception is the space-to-ground
link, in which capacities of 100 Mbps are currently available. While
magnetic recording media can handle I/0 rates of 107 bps, the annual
volume of 1014 bits will require over 100,000 tapes per year (CD ROMs
cannot handle input rates of 107bps). Near-real-time processing and
distribution of data to users still might be feasible as long as a single
user does not demand access to all the data over extended periods of time.
Processing speeds of 100 MIPS to handle level-zero processing, as well as
storage requirements of over 100,000 PSUs per year, present some major
problems using projections of current technology.
Data rates of the order of 108 bps present possibly insurmountable
problems and challenges. Processing speeds of over 1,000 MIPS, and I/0
rates of 100 Mbps into and from storage media, are difficult to achieve
unless parallel-processing techniques are used. Even then, the number of
PSUs will be of the (unmanageable) order of 106 units per year. Near
real time distribution of data to users may not be economically feasible
at these rates.
We do not anticipate an exponential growth in the I/0 rates and stor-
age capacities of magnetic media (or CD ROMs), or throughput rates of con-
temporary production networks. Specially designed multichannel magnetic
recorders or very-high-speed integrated circuit (VHSIC) memories may pro-
vide a means to capture and process short bursts of data at rates of 108
bps. However, current technology, as well as what is projected to be
available in the time frame being considered, cannot support the process-
ing, storage, and distribution of data at sustained rates of 108 bps or
higher.
The need for data rates of 108 bps or higher originates from high-
resolution imaging sensors, such as multichannel spectral scanners (MSS),
thematic mappers (TM), and synthetic aperture radars (SAR). There are two
possible solutions to the probe ems created by these high-data-rate sen-
sors. First, image data is highly redundant and data-compression schemes
can be used to reduce the data rates by almost one to two orders of magni-
tude. Commercial coder-decoder (CODEC) devices are currently used in a
variety of applications for data compression and reconstruction. In NASA
systems, compression may take place on the space platform or on the ground
where the level-zero processing is done. Fairly simple spatial and
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spectral compression algorithms can be applied to data streams of BOB
bps to reduce the rate to lob tO 107 bps.
While compression algorithms have been developed and applied to MSS
image data, new algorithms need to be developed for data from SAR and
other sensors whose statistics are quite different from those of MSS data.
Once successful algorithms are applied to the outputs of high-data-rate
sensors, the resulting reduced data rates can be handled with existing
technology. The development and application of data-compression
techniques should be coordinated carefully with the user community, which
traditionally takes the view that nobody should "mess around" with the
data. They should be convinced that some trade-offs have to be made in
order to maintain high throughputs over long periods of time. If the
option to transmit uncompressed data over short periods of time, when
needed, is maintained, the Committee believes that users can be convinced
to accept compressed data (user involvement was discussed in Chapter V).
The data-compression issue may have to be looked at in the broader
context of data or bandwidth management. Issues such as compressing data
onboard versus compressing it on the ground, and using an "expert system"
onboard to extract information and make decisions about how much data from
each instrument to transmit to the ground, need continued study and
analysis. At the higher data rates (>108 bps), the onboard processing
requirements to implement any kind of "expert system" might require
processing speeds in excess of I'000 MIPS and may not be cost-effective.
The cost trade-off between introducing additional processing requirements
and savings that might result from reduced costs for storage and
distribution must be analyzed carefully.
An alternate approach is to consider analog (or hybrid) recording
techniques for storage purposes. Consider, for example, a standard TV
signal which has a bandwidth of about 5 Megahertz (MHz). If this signal
is digitized, the data rate required will be of the order of 108 Mbps
without compression. Digital recording at this rate for as little as an
hour wild produce hundreds of digital magnetic tapes. However, several
hours of the analog TV signal can be recorded on a single $4 VHS tape with
a $200 recorder! Now, while digitizing facilitates easy multiplexing and
transmission over long and noisy communication links, there are no signif-
icant advantages that warrant digital recording. The CD ROM technology
does not provide any attractive solution to high-volume, low-demand
applications. It is most effective for low, continuous throughput and
high demand (several hundred copies distributed) applications.
The Committee sees promise in the use of commercially available
recording technologies such as Jarge-bandwidth analog, hybrid magnetic
recording, or optical technologies. While analog or hybrid recording
using magnetic tapes provides high throughput and capacities, random
access to recorded data is not yet possible. Laser-vision and Jaser-video
disks offer capacities and throughputs that are much higher than those of
CD ROMs. Even though the throughput and capacities of laser-vision and
laser-video disks may not be as high as analog magnetic tapes, they do
46
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provide random-access capabilities. The throughput and capacities of
video disks are an order of magnitude higher than those of CD ROMs; hence,
the video-disk technology should be monitored.
Limitations of Commercial Database Management Systems {DBMS). Based
on briefings from NASA personnel, the Committee understands that during
the next decade, NASA's mission-specific data systems will be replaced by
more generic, multi-discip~inary DBMSs. Data systems can be characterized
as those where the users of the system are responsible for providing all
desired management of the data, whereas DBMSs provide generic management
capabilities as an integral part of the database system. The commercial
world successfully underwent this transition some years ago, and it is
evident that the engineering and scientific worlds are undergoing a
similar transition today. Equally important, major standardization
activities relative to DBMSs and associated capabilities (e.g., query
languages, report writing facilities) are gaining in momentum. The advent
of relationa1-based systems has been a major factor in the drive toward
standardization and wild provide a vendor-independent base for future
database management systems technology. The Committee also believes that
OSSA and its constituent program and project offices should focus on
using, to the greatest extent possible, commercial~y-available DBMSs or
derivatives thereof, rather than spend excessive amounts of resources in
developing their own.
However, while commercially available DBMSs will provide a comprehen-
sive set of data management facilities, there remain a number of areas in
which these systems fall short of meeting the needs of the engineering and
scientific communities for management of large volumes of space-derived
data. In conjunction with NOAA, NSF, and the community of vendors and
standards organizations, NASA/OSSA should focus on this shortcoming, and
encourage the private sector and the standards organizations to develop
appropriate solutions. Some of this is already being done: the agreement
reached between NASA and NSF in NSF's supercomputer initiative is a major
step in this direction. Many of the supercomputer centers wild be extend-
ing commercially available database management systems to provide those
facilities required for the target engineering and scientific communities.
Additional efforts of this type are required.
The Committee believes the major areas to be addressed are the
following:
l. Performance. Much of the past reluctance of the engineering and
scientific communities to adopt commercially available DBMSs has
been the Jack of numerically intensive computational performance
available through the use of these systems. There has been an
acceptance of this deficiency and much work is now underway to
provide the necessary levels of performance. OSSA and its
constituent user communities should quantify their performance
requirements and make them known to vendors and other interested
parties (e.g., the NSF).
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2. Very large databases. Closely associated with the performance
question discussed above is the question of the ability to handle
very large databases. Traditional, commercially oriented DBMSs
have not proven themselves to be particularly well suited to
dealing with the massive amounts of data that normally are dealt
with by the engineer or scientist. However, this shortcoming has
indeed been recognized and much research is
improve the ability of DBMSs to deal effectively
databases, either directly or through the use of
processors.
currently under way to
with very large
auxiliary
3. Data definition capabilities. Commercial DBMSs have focused pri-
marily on data-definitional facilities that have been oriented to
the commercial world. These have proven not to be adequate for
the engineering or scientific user. OSSA should understand better
the needs of its user base in this area and transmit those needs
to the appropriate standards organizations and vendors.
4. Data interchange. To achieve even a primitive level of interoper-
ability, data interchange agreements must be formulated and agreed
upon. These agreements or standards must be as non-constricting
as possible; therefore, the Committee recommends that these stan-
dards be based on the notion of self-defining data (that is, data
wherein the definition of the content of the data record is con-
tained within the record itself). While we saw some indication of
a beginning of this in the EOS project, it needs to be focused
upon on a much broader base with a much higher assigned priority.
5. Directories and carats. The Committee has previously noted in
this report the central rode to be played by directories. We
believe that effective and efficient directory management capabi,
ities (including abilities to these directories) wild be a key
factor in achieving systems interoperability. User requirements
for both directory content and directory management should be
gathered, analyzed, and submitted to vendors and appropriate
standards organizations for consideration and adoption.
6. Distributed Systems. It is inevitable that NASA scientists will
be involved at a globe] level with a hierarchy of systems, with
much distribution of both data and processing being both desirable
and necessary. Fundamental architectural decisions, accommodating
heterogenous systems and vendors, should be dealt with immediate-
ly. For example, will control information and responsibility be
centrally managed or distributed? What will be the capabilities
for shipping data to work and/or work to data?
48
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Representative terms from entire chapter:
magnetic recording
