Quality control of oceanographic insitu data from
Argo floats using climatological convex hulls
Authors
T.V.S.Udaya Bhaskar, R.Venkat Shesu, Timothy P.Boyer,
E. Pattabhi Rama Rao
Source
MethodsX 4(2017)469-479
Abstract
A new method of identifying anomalous oceanic temperature and salinity(T/S) data from Argo profiling floats is
proposed. The proposed method uses World Ocean Database 2013 climatology to classify good against anomalous
data by using convex hulls. An n-sided polygon(convex hull) with least area encompassing all the climatological
points is constructed using Jarvis March algorithm.Subsequently Points In Polygon(PIP) principle implemented
using ray casting algorithm is used to classify the T/S data as within or without acceptable bounds.It is observed
that various types of anomalies associated with the oceanographic data viz.,spikes,bias, sensor drifts etc can be
identified using this method.Though demonstrated for Argo data it can be applied to any oceanographic data.
The patterns of variation of the parameter(temperature or salinity) corresponding to a particular depth,along
the longitude or latitude can be used to build convex hulls.
This method can be effectively used for quality control by building Convex hulls for various observed depths
corresponding to biogeochemical data which are sparsely observed.
Paper No
2
Publication ID : 676 & Year : 2017
Title
Detecting and Correcting the Degradations of Sensors on Argo Floats Using Artificial Neural Networks.
Authors
T Satyanarayana Raju, TVS Udaya Bhaskar, J Pavan Kumar, K S Deepthi
Source
Computer Communication, Networking and Internet Security, 299-308
Abstract
Argo floats are autonomous floats designed to measure temperature and salinity of the world oceans. Once deployed these floats goes to as deep as 2000 meters and while coming up measure temperature and salinity of the underlying ocean automatically. These floats act as a substitute to the ship-based data sets and currently as many as ~3800 are active in the global oceans. These instruments being autonomous in nature, measure and transmit data seamlessly irrespective of the weather, season, and region. However, the salinity sensors on these floats are sensitive to bio-fouling and can cause degradation to the data. As these are one time deployed and data is continuously obtained they are not available for calibration unlike the instruments on the ship. In this work ANN is used to check the degradation of the sensors and correct the same so that the data can be use in scientific analysis.
Paper No
3
Publication ID : 675 & Year : 2016
Title
USE OF CONVEX HULL FOR DETECTION OF OUTLIERS IN
OCEANOGRAPHIC DATA PERTAINING TO INDIAN OCEAN.
International Journal of Advances in Electronics and Computer Science, Volume-3, Issue-8, Aug.-2016.
Abstract
This work discusses a new method of identifying erroneous surface meteorology data using ICOADS data. An
'n' sided polygon (convex hull) with least area encompassing all the points is constructed based on the Jarvis March
algorithm. The periphery points from the clusters formed while plotting the parameter (e.g.: Air temperature, humidity)
against longitude and latitudes is used for building the polygons. Subsequently, Point-In-Polygon (PIP) principle is used to
classify the data as in or out of the polygon. It is observed that all possible outlier associated with the data can be identified
using this method.
Paper No
4
Publication ID : 674 & Year : 2016
Title
Generation and Validation of two Day Composite Wind Fields from Oceansat-2 Scatterometer.
Authors
Tata V. S. Udaya Bhaskar & Chiranjivi Jayaram & Saurabh Bansal &
K Krishna Mohan & Debadatta Swain
Source
Indian Soc Remote Sens
DOI 10.1007/s12524-016-0566-5
Abstract
The Oceansat-2 scatterometer (OSCAT) of the
Indian Space Research Organization (ISRO), provides surface
wind speed and direction with a spatial resolution of
50 km ÿ 50 km. With a revisit time of 2 days it had provided
ocean surface wind vectors over the global oceans. In the present
work, an attempt has been made to generate two day composite
of OSCAT wind vectors using Data-Interpolating
Variational Analysis (DIVA) and compare them with daily
composite winds to check how better is the two day composites
in comparison to daily composites. The daily and two days
composite wind vectors of zonal (U) and meridional (V) components
have been validated with wind measurements from in
situ buoys and Advanced Scatterometer (ASCAT) for the year
2012 over the tropical Indian Ocean region. The statistical comparison
with the in situ measurements and ASCAT has shown
that the two-day OSCAT wind composites are slightly better
than the daily composite winds. The improvement in the statistics
can be attributed to the use of ascending and descending passes pertaining to two days which results in fewer gaps between
passes, thereby reducing the interpolation errors.
Paper No
5
Publication ID : 673 & Year : 2016
Title
Relation between Sonic Layer and Mixed layer depth in the Arabian Sea
Authors
TVS Udaya Bhaskar, Debadatta Swain
Source
Indian Journal of Geo-Marine Science
Vol. 45(9), September 2016, pp.
Abstract
Seasonal evolution of the sonic layer depth and its relation to mixed layer depth in the Arabian Sea is studied. Monthly sonic layer depth climatology is constructed using Argo temperature and salinity and compared with mixed layer depth. Sonic layer depth showed semiannual variability with peaks during June ⿿ August and December ⿿ February and lows during pre and post monsoon season. Sonic layer depth is observed to be shallower than mixed layer depth over most of the Arabian Sea except in the southeastern Arabian Sea during winter owing to temperature inversions. Sonic layer and mixed layer depth is observed to have high correlation (> 0.85) over most of the Arabian Sea indicating a good relationship between them, except in south eastern Arabian Sea. SLD is found to be deeper than MLD only in the southeastern AS (SEAS) during the winter season due to the presence of temperature inversions (TI) which are common phenomenon during that period. Advection of cooler low-salinity water over warmer salty SEAS water leads to the formation of TI in SEAS. Sound velocity being sensitive to temperature, results in deepening of SLD in this region. This can be used to understand relation between them to a great degree of accuracy and estimate one from the other.
Paper No
6
Publication ID : 677 & Year : 2016
Title
Spatio-temporal evolution of chlorophyll-a in the Bay of Bengal: a remote sensing and bio-argo perspective.
Authors
TVS Udaya Bhaskara, Chiranjivi Jayaram, E P Rama Rao and K H Rao
Source
SPIE Asia-Pacific Remote Sensing, 98780Z-98780Z-6
Abstract
Argo floats equipped with sensors to measure Dissolved Oxygen, Chlorophyll-a and backscattering are deployed in the
Arabian Sea, Bay of Bengal and Southern Indian Ocean as part of Indian Argo program. In this study, abnormal
chlorophyll-a bloom observed by a float with WMO ID 2902086 deployed in the south central Bay of Bengal is
analyzed. High concentration of chlorophyll > 0.8 mg/l is observed during December 2013. This period is also associated
with drop in temperature and increase in salinity. Analysis of data from the bio-Argo float has shown the impact of many
cyclones and depressions that occurred during the period. Of particular importance is cyclone ⿿Madi⿿, which passed very
near to the position of mentioned float, during December 2013. This is also evident from the satellite based wind
observations from OSCAT through curl of wind stress and Ekman pumping. The sub-surface chlorophyll bloom is
substantiated by the surface chlorophyll-a values of MODIS during the period. Intense mixing caused due to the passage
of cyclone might have resulted in mixing of subsurface waters thereby breaking the stratification of otherwise stable
surface waters of Bay of Bengal, enhancing the nutrient supply, which resulted in strong chlorophyll bloom. The
subsurface chlorophyll structure of Bay of Bengal and its variability during the passage of cyclone is for the first time
revealed by the floats equipped with biological sensors. This work reveals the synergistic application of in-situ (Bio-
Argo) and satellite data to monitor the changes in subsurface structure during the passage of cyclones.
Paper No
7
Publication ID : 678 & Year : 2016
Title
Relation between Tropical Cyclone Heat Potential and Cyclone
Intensity in the North Indian Ocean.
Authors
B. Jangir, D. Swain and T.V.S. Udaya Bhaskar
Source
SPIE Asia-Pacific Remote Sensing, 988228-988228-7
Abstract
Ocean Heat Content (OHC) plays a significant role in modulating the intensity of Tropical Cyclones (TC) in terms of the
oceanic energy available to TCs. TC Heat Potential (TCHP), an estimate of OHC, is thus known to be a useful indicator
of TC genesis and intensification. In the present study, we analyze the role of TCHP in intensification of TCs in the
North Indian Ocean (NIO) through statistical comparisons between TCHP and Cyclone Intensities (CI). A total of 27
TCs (20 in the Bay of Bengal, and 7 in the Arabian Sea) during the period 2005-2012 have been analyzed using TCHP
data from Global Ocean Data Assimilation System (GODAS) model of Indian National Center for Ocean Information
Services and cyclone best track data from India Meteorological Department. Out of the 27 cyclones analyzed, 58%
(86%) in the Bay (Arabian Sea) have negative correlation and 42% (14%) cyclones have positive correlation between CI
and TCHP. On the whole, more than 60% cyclones in the NIO show negative correlations between CI and TCHP. The
negative percentage further increases for TCHP leading CI by 24 and 48 hours. Similar trend is also seen with satellite
derived TCHP data obtained from National Remote Sensing Center and TC best track data from Joint Typhoon Warming
Centre. Hence, it is postulated that TCHP alone need not be the only significant oceanographic parameter, apart from sea
surface temperature, responsible for intensification and propagation of TCs in the NIO.
Paper No
8
Publication ID : 670 & Year : 2015
Title
Observed interannual variability of near⿐surface salinity in the Bay of Bengal
Authors
Vimlesh Pant, M. S. Girishkumar, T. V. S. Udaya Bhaskar, M. Ravichandran, Fabrice Papa,
and V. P. Thangaprakash
Source
J. Geophys.
Res. Oceans, 120, doi:10.1002/
2014JC010340.
Abstract
An in situ gridded data of salinity, comprising Argo and CTD profiles, has been used to study
the interannual variability of near-surface salinity (within 30 m from sea surface) in the Bay of Bengal (BoB)
during the years 2005⿿2013. In addition to the broad agreement with earlier studies on the north-to-south
gradient of surface salinity and general features of seasonal variability of salinity, the data also revealed few
episodes of enhanced freshening in the BoB. The observations showed distinct anomalous low salinity (< 2
psu) waters in the northern BoB during June⿿February of the years 2006⿿2007 (Y67), 2011⿿2012 (Y12), and
2012⿿2013 (Y23). The anomalous freshening during these years showed similar life cycle, such as, it starts in
the northern BoB during July⿿September of current summer and extends up to February⿿March of next
winter with a southward propagation. Analysis showed that the oceanic and atmospheric conditions associated
with positive Indian Ocean Dipole (pIOD) lead to these freshening events, and IOD rather than El Ni~no/
Southern Oscillation (ENSO) controls the interannual variability of salinity in the BoB. The mixed layer salt
budget analysis indicated the dominant role of local fresh water flux (horizontal advection) on the observed
salinity tendency during summer (winter) monsoon season. Enhanced precipitation associated with pIOD
lead to enhanced freshening in northern BoB during June⿿September, which remained to this region with
prevailing summer monsoon circulation. The weakening or absence of southward east India coastal current
(EICC) during October⿿December of these freshening years trapped anomalous freshwater in the northern
BoB.
Paper No
9
Publication ID : 672 & Year : 2015
Title
Heat content of the Arabian Sea Mini Warm Pool is increasing.
Authors
P. V. Nagamani, M. M. Ali, G. J. Goni, T. V. S. Udaya Bhaskar, J. P. McCreary, R. A. Weller, M. Rajeevan,
V. V. Gopala Krishna and J. C. Pezzullo
Source
Atmos. Sci. Let., 10.1002/asl.596
Abstract
Sea surface temperature in the Arabian Sea Mini Warm Pool has been suggested to be one of
the factors that affects the Indian summermonsoon. In this paper, we analyze the annual ocean
heat content (OHC) of this region during 1993⿿2010, using in situ data, satellite observations,
and a model simulation. We find that OHC increases significantly in the region during this
period relative to the north Indian Ocean, and propose that this increase could have caused
the decrease in Indian Summer Monsoon Rainfall that occurred at the same time.
Paper No
10
Publication ID : 671 & Year : 2015
Title
Evaluation of Aquarius sea surface salinity with Argo sea surface salinity in the Tropical Indian Ocean.
Authors
T.V. S. Udaya Bhaskar and Chiranjivi Jayaram
Source
IEEE GEOSCIENCE AND REMOTE SENSING LETTERS, 10.1109/LGRS.2015.2393894
Abstract
The performance of sea surface salinity (SSS) obtained
from the Aquarius satellite is evaluated. Daily, weekly, and
monthly Aquarius SSS data between September 2011 and August
2013 from the tropical Indian Ocean (TIO) are compared with
the surface most salinity observations (< 5 m) from Argo floats.
Statistics between a daily reporting Argo float (WMO 2901329)
and daily Aquarius SSS resulted in a root-mean-square error
(RMSE), a bias, and a correlation of 0.32 psu, 0.02 psu, and 0.81,
respectively. Weekly 1 ÿ 1 spatial resolution SSS was produced
from the Argo data using variational analysis and was compared
with Aquarius SSS data. RMSE was observed to be between 0
and 0.25 psu over most of the region. Bias was observed to be
within 0.3 psu everywhere, except in the southeastern Arabian Sea
and the southeastern TIO. Good correlation (> 0.6) was observed
everywhere, except the coast of Oman, western equatorial Indian
Ocean, and south of 20 S. A seasonal comparison has also revealed
that both Aquarius and Argo are in agreement; in addition,
the Aquarius SSS clearly shows the seasonal salinity cycle of the
TIO.
Paper No
11
Publication ID : 668 & Year : 2014
Title
On the possible use of satellite fixed positions for Argo profiles in case of GPS failures.
Authors
R U V N SATISH, T V S UDAYA BHASKAR, N SURESH KUMAR, M RAVICHANDRAN, K DINESH
AND ASHOK KUMAR
Source
International Journal of Earth Sciences and Engineering, Vol 08 (02),
Abstract
Indian National Centre for Ocean Information Services (INCOIS) had deployed Iridium based Provor
Bio-Argo floats obtained from NKE Instrumentation, France. These floats are fitted with GPS for obtaining accurate
position of the Argo profiles. However there are cases where in the GPS fitted with the Argo floats tend to give
wrong coordinates of profile position owing to unknown reasons. In the present work we discussed the possibilities
of using the Iridium satellite fixed position as a substitute of GPS fixed locations in place of wrong GPS positions.
For this, statistical analysis was done by comparing the GPS and Iridium satellite fixed profiles positions of 258
profiles from 5 floats which had no problem with the GPS. For each comparison, the GPS fixed position with least
Circular Error Probability (CEP) radius was chosen. It was observed that CEP radii are relatively consistent with
distances between GPS and Iridium satellite fixes with a correlation of 0.85. The study suggests that on an average
the Iridium satellite based positions tend to differ from the GPS fixed positions by 0.09°. On the whole CEP radii are
found to be consistent with the difference between Iridium satellites and GPS fixed positions. Based on this we
suggest a quality flag of 2 (implying probably good) for positions with CEP radius less than or equal to 4 Km and
flag 4 (implying bad) for all other positions.
Paper No
12
Publication ID : 667 & Year : 2014
Title
Observed oceanic response to tropical cyclone Jal from a moored buoy in the south-western Bay of Bengal
Authors
M. S. Girishkumar & K. Suprit & Jayaram Chiranjivi &
T. V. S. Udaya Bhaskar & M. Ravichandran &
R. Venkat Shesu & E. Pattabhi Rama Rao.
Source
Ocean Dynamics
DOI 10.1007/s10236-014-0689-6
Abstract
Upper oceanographic and surface meteorological
time-series observations from a moored buoy located at
9.98°N, 88°E in the south-western Bay of Bengal (BoB) were
used to quantify variability in upper ocean, forced by a tropical
cyclone (TC) Jal during November 2010. Before the passage of
TC Jal, salinity and temperature profiles showed a typical BoB
post-monsoon structure with relatively warm (30 °C) and lowsaline
(32.8 psu) waters in the upper 30- to 40-m layer, and
relatively cooler and higher salinity (35 psu) waters below.
After the passage of cyclone, an abrupt increase of 1 psu
(decrease of 1 °C) in salinity (temperature) in the near-surface
layers (up to 40-m depth) was observed from buoy measurements,
which persisted up to 10⿿12 days during the relaxation
stage of cyclone.Mixed layer heat budget analysis showed that
vertical processes are the dominant contributors towards the
observed cooling. The net surface heat flux and horizontal
advection together contributed approximately 33%of observed
cooling, during TC Jal forced stage. Analysis showed the
existence of strong inertial oscillation in the thermocline region
and currents with periodicity of ⿼2.8 days. During the relaxation
stage of the cyclone, upward movement of thermocline in
near-inertial frequencies played significant role in mixed layer temperature and salinity variability, by much freer turbulent
exchange between the mixed layer and thermocline.
Paper No
13
Publication ID : 669 & Year : 2014
Title
Daily composite wind fields from Oceansat-2 scatterometer
Authors
Chiranjivi Jayarama, T V S Udaya Bhaskar, Debadatta Swain, Eluri Pattabhi
Rama Rao, Saurabh Bansal, Dibyendu Dutta, and Kalluri Hanumantha Rao
Oceansat-2 scatterometer (OSCAT) is an active microwave sensor, intended to
provide ocean surface wind vectors over the global oceans. In the present work,
an attempt has been made to generate daily composites of OSCAT Level-3 (L3)
wind vectors using Data-Interpolating Variational Analysis (DIVA) method from
ascending and descending passes over the Indian Ocean region. This could be
useful for operational purposes and in generating value-added products like wind
stress and curl of wind stress. The daily composite wind vectors of zonal (U) and
meridional (V) components have been validated by comparing with Advanced
Scatterometer (ASCAT) and wind from in situ buoys for the year 2012. Wind
composites thus generated using DIVA are found to match well with in situ, and
ASCAT wind products. Minor deviations are observed with respect to ASCAT
wind, which could be attributed to the difference in interpolation techniques used
for the two scatterometer products. Given that the repeat period of ASCAT is
5 days and that of OSCAT is only 2 days, OSCAT wind products could be
conveniently used for real-time met-ocean studies.
Paper No
14
Publication ID : 663 & Year : 2013
Title
INCOIS Live Access Server: A Platform for Serving the Geospatial Data of Indian Ocean
Authors
R Devender, TVS Udaya Bhaskar, E Pattabhi Rama Rao
BV Satyanarayana
Source
International Journal of Oceans and Oceanography, Volume 7, Number 2 (2013), pp. 143-151.
Abstract
The INCOIS Live Access Server (I-LAS) was setup at Indian National Centre
for Ocean Information Services to effectively deliver diversified geospatial
products pertaining to Indian Ocean. The I-LAS provides free access to full
suite of satellite-derived data products viz., sea surface temperature (SST),
surface chlorophyll, surface wind products and number of products derived
from objectively analyzed in-situ data. Further model analysis products from
GODAS-MOM are also made available. Additionally climatological data sets
from World Ocean Atlas 2009 are also made available for inter-comparison
and generation of anomalies. Various functionalities for on the fly
visualization and downloading of data are in built in to the LAS along with
OpenDAP data sharing. Some examples of data usage from the LAS are also
presented. It is observed that INCOIS LAS is being extensively used by
various users and statistics of data usage is monitored on a regular basis and
100% uptime is maintained.
Paper No
15
Publication ID : 666 & Year : 2013
Title
GUI based interactive system for Visual Quality Control of Argo data
Authors
GUI based interactive system for Visual Quality Control of Argo data
Source
Indian Journal of Geo-Marine Sciences, Vol 42(5), September 2013, pp 580 - 586.
Abstract
Argo program is aimed at maintaining an array of 3000 free drifting floats which measure temperature and salinity (T/S). In this work, a PC-based system developed for visualization and quality control of T/S profiles obtained from Argo floats is described. The system, coded in Java, is user interactive and runs on Windows platform. By default the Argo T/S profiles pass through 19 automatic checks and quality flags are assigned. Using the system, T/S profiles that failed the automatic Argo tests undergo visual review. This visual review is done to determine whether automatic Argo tests were excessively flagging good measurements as bad or vice-versa, to identify possible modifications to automatic Argo tests and to determine whether additional tests are necessary to catch problems that could not be detected by the existing tests. Visual review is done by comparing with 1° X 1° monthly climatology from WOA01. Profile records deviating beyond 2 standard deviations from the mean are flagged as bad. Provision is also given to compare individual T/S profiles with previous 5 profiles via a waterfall plot.
Paper No
16
Publication ID : 665 & Year : 2013
Title
Open Source Architecture for Web-Based Oceanographic Data Services.
Authors
R Venkat Shesu, TVS Udaya Bhaskar*, E Pattabhi Rama Rao, R Devender, and
T Hemasundar Rao
Source
Data Science Journal, Volume 12, 6 September 2013
47
Abstract
A GIS for ocean data applications named "Ocean Data and Information Systems (ODIS)" was designed and developed. The system is based on the University of Minnesota MapServer, an open source platform for publishing spatial data and interactive mapping applications to the web with MySQL as the backend database server. This paper discusses some of the details of the storage and organization of oceanographic data, methods employed for visualization of parameter plots, and mapping of the data. ODIS is conceived to be an end-to-end system comprising acquisition of data from a variety of heterogeneous ocean platforms, processing, integration, quality control, and web-based dissemination to users for operational and research activities. ODIS provides efficient data management and potential mapping and visualization functions for oceanographic data.
Paper No
17
Publication ID : 664 & Year : 2013
Title
Comparison between Argo-derived sea surface temperature and microwave sea surface temperature in tropical Indian Ocean
Authors
TATA V. S. UDAYA BHASKAR*, CHIRANJIVI JAYARAM and
ELURI PATTABHI RAMA RAO
Source
Remote Sensing Letters
Vol. 4, No. 2, February 2013, 141⿿150
Abstract
A comparison between in situ and microwave satellite-derived sea surface temperature
(SST) for the tropical Indian Ocean (TIO) during January 2009⿿December
2010 is presented. All available in situ temperatures close to the surface (⿼5 m)
from Argo profiling floats are used in this study. Weekly 0.25 ÿ0.25 spatial resolution
SST was produced from these Argo in situ data using the Data-Interpolating
Variational Analysis (DIVA) method. This weekly Argo sea surface temperature
(ASST) is compared with Tropical Rainfall Measuring Mission Microwave
Imager (TMI)-retrieved Sea Surface Temperature (TMISST) and available blended
Optimum-Interpolation Sea Surface Temperature (OISST) product, at selected
regions encompassing the north, central and southern TIO. The results indicate
a bias and root mean square error (RMSE) of ⿿0.02C and 0.45C between ASST
and OISST, whereas the bias and RMSE between ASST and TMISST is observed
to be 0.11C and 0.32C, respectively. The correlation coefficient (r) between ASST
and OISST is observed to be 0.980, whereas r between ASST and TMISST is
observed to be 0.985.
Paper No
18
Publication ID : 662 & Year : 2012
Title
Validation of satellite-derived tropical cyclone heat potential with in situ observations in the North Indian Ocean.
Authors
PULLAIAHGARI V. NAGAMANI, MEER M. ALI, GUSTAVO J. GONI,
PEDRO N. DINEZIO, JOHN C. PEZZULLO,
T. V. S. UDAYA BHASKAR, V.V GOPALAKRISHNA
and NISHA KURIAN
Tropical cyclone heat potential (TCHP) is an important ocean parameter influencing
cyclones and hurricanes. The best approach for computing TCHP is to use
in situ measurements. However, since in situ data have both spatial and temporal
limitations, there is a need for satellite-based estimations. One potential solution
is to use sea surface height anomalies (SSHAs) from altimeter observations.
However, any estimation derived from satellite measurements requires extensive
regional validation. In this letter, we compare satellite-derived TCHP values with
those estimated using in situ measurements of the North Indian Ocean collected
during 1993⿿2009. All the available measurements collected from the conductivity
temperature and depth (CTD) profiler, expendable CTD profiler (XCTD),
bathythermograph (BT), expendable BT (XBT) and Argo floats were used to estimate
in situ derived TCHP values. TCHP estimations from satellite observations
and in situ measurements are well correlated, with coefficient of determination R2
of 0.65 (0.76) and a scatter index (SI) of 0.33 (0.25) on a daily (monthly) basis for
the North Indian Ocean.
Paper No
19
Publication ID : 660 & Year : 2012
Title
Oxycline variability in the central Arabian Sea: An Argo-oxygen study.
Dissolved oxygen concentration in the oceanic waters plays a vital role in the global carbon cycle. The
addition of oxygen sensors in the ongoing Argo programme could revolutionize our understanding of the
ocean's role in climate change. Here we present a first analysis of the oxygen profiles obtained from Argo float
2900776, deployed in the oxygen minimum zone of the central Arabian Sea, one of the thickest oxygen
minimum zones in the world ocean. Our study shows perennial oxygen minima in the sub-surface waters of
the central Arabian Sea with strong inter-annual and intra-seasonal variability. The depth of the oxycline
varies from 60 to 120 m but occasionally it may be as shallow as 40 m. It appears from the present data set
that in the southeastern Arabian Sea the low oxygen water shoals up during the early winter monsoon and it
is largely controlled by remote forcing. Small scale localized high wind events can cause further shoaling of
the oxycline.
Paper No
20
Publication ID : 659 & Year : 2012
Title
A new atlas of temperature and salinity for the North Indian Ocean.
Authors
A Chatterjee, D Shankar, S S C Shenoi, G V Reddy, G S Michael,
M Ravichandran, V V Gopalkrishna, E P Rama Rao,
T V S Udaya Bhaskar and V N Sanjeevan
Source
J. Earth Syst. Sci. 121, No. 3, June 2012, pp. 559⿿593.
Abstract
The most used temperature and salinity climatology for the world ocean, including the Indian Ocean,
is the World Ocean Atlas (WOA) (Antonov et al 2006, 2010; Locarnini et al 2006, 2010) because of
the vast amount of data used in its preparation. The WOA climatology does not, however, include
all the available hydrographic data from the Indian Exclusive Economic Zone (EEZ), leading to the
potential for improvement if the data from this region are included to prepare a new climatology. We
use all the data that went into the preparation of the WOA (Antonov et al 2010; Locarnini et al
2010), but add considerable data from Indian sources, to prepare new annual, seasonal, and monthly
climatologies of temperature and salinity for the Indian Ocean. The addition of data improves the
climatology considerably in the Indian EEZ, the differences between the new North Indian Ocean Atlas
(NIOA) and WOA being most significant in the Bay of Bengal, where the patchiness seen in WOA, an
artifact of the sparsity of data, was eliminated in NIOA. The significance of the new climatology is that
it presents a more stable climatological value for the temperature and salinity fields in the Indian EEZ.
Paper No
21
Publication ID : 658 & Year : 2012
Title
Application of Satellite Products to Study Upwelling, Chlorophyll and Mixed Layer Depth of Southeastern Arabian Sea
Authors
C Jayaram, BTVS Udaya, JK Ajith, AN Balchand.
Source
The International Journal of Ocean and Climate Systems 3 (2), 97-108
Abstract
The role of wind stress in modulating upwelling and subsequent changes in mixed layer
depth and chlorophyll concentration in southeastern Arabian Sea are studied for the
period encompassing 2000 ⿿ 2008. During southwest monsoon season favoring
upwelling in this region, it is observed that decrease in wind stress is always followed by
an increase in chlorophyll concentration with approximately two weeks delay,
accompanied by the shoaling of mixed layer depth, whereas the opposite is observed
during high wind stress periods. This is attributed to the mixing and entrainment of
nutrients into the euphotic zone which enable increase in surface chlorophyll and thereby
boosting the primary productivity of the region. Wavelet analysis is used to deduce the
temporal variability of winds, chlorophyll and mixed layer for the region. A time lag of
2 weeks is observed between the decrease in wind stress followed by a high in the surface
chlorophyll concentration, often well captured by satellite. Another interesting
observation is the bimodal variability of chlorophyll-a concentration during summer
monsoon is observed in this region which was hitherto unnoticed. This spatial and
temporal relation between wind, chlorophyll and mixed layer depth can provide valuable
insight towards future studies on upwelling induced productivity for this region.
Paper No
22
Publication ID : 661 & Year : 2012
Title
A note on three way quality control of Argo temperature and salinity profiles - A semi-automated approach at INCOIS.
Authors
T. V. S. UDAYA BHASKAR, E. PATTABHI RAMA RAO, R. VENKAT SHESU and R. DEVENDER.
Source
International Journal of Earth Science and Engineering, Vol 5 (06), 2012.
Abstract
A three way semi-automated quality control system established at Indian National Centre for Ocean
Information Services (INCOIS) for quality control of near real time temperature and salinity profiles obtained from
Argo deployed by India as well as other countries in the Indian Ocean is presented. At the outset, all the temperature
and salinity profiles are passed through 18 automated quality checks as suggested by the International Argo Data
Management Team (ADMT). Further, all the profiles are utilized in generating objectively analyzed product. Bad
profiles appearing as bulls eye are automatically rejected based on preset statistics. These bad profiles are then
visually checked (which requires manual intervention) using a visual quality control tool developed in house, for
their correctness. At the end of the quality control procedures, 10days and monthly objectively analyzed gridded
product of 1° X 1° resolution for the period 2002 - 2012 is generated and is made freely available on INCOIS Live
Access Server (las.incois.gov.in) in NetCDF format.
Paper No
23
Publication ID : 357 & Year : 2011
Title
Validation of Mixed Layer Depth Derived using Satellite Data and Wave Model with In-Situ Observations
Authors
K. Annapurnaiah, T.V.S. Udaya Bhaskar , T.M. Balakrishnan Nair and Satyabana Das
Source
Volume 5 Number 1, International Journal of Oceans and Oceanography, pp 23 - 34.
Abstract
The seasonal variability of mixed layer depth (MLD) in the northern Indian
Ocean (40E 105E and 2S 30N) was estimated from empirical relation
using wind speed from QuickSCAT and wave parameters (significant wave
height and wave period) obtained from MIKE-21 SW model. MLD estimated
from this empirical model is compared with MLD estimated from Argo
temperature and salinity profiles. The extent of mechanical mixing with in the
top layer of water by local wind and wave activity is studied using this simple
statistical predictive method. The correlation coefficient (R) between in-situ
MLD and model MLD is found to be 0.52, 0.67, 0.34 and 0.04 for premonsoon,
southwest monsoon, post-monsoon and northeast monsoon
respectively. By and large, the proposed empirical model could be used to
simulate the MLD and its trend by considering wind and wave parameters, and
can act as a useful tool at times when there are sparse in-situ observations.
Paper No
24
Publication ID : 356 & Year : 2011
Title
Argo Data and Products of Indian Ocean for Low Bandwidth Users
Authors
G. Geetha, T.V.S. Udaya Bhaskar and E. Pattabhi Rama Rao
Source
Volume 5 Number 1, International Journal of Oceans and Oceanography, pp 1 - 8
Abstract
Argo is an internationally coordinated activity aimed at characterizing both the temperature and salinity structure of the mid- and upper-ocean through deployment of autonomous profiling floats and making the data available to users with in 24 hrs of reception. To cater to wide users of oceanographic data, mainly from the universities, who lack high bandwidth internet connections, an Argo Data Explorer (ADE) on Argo data and products for the Indian Ocean is prepared. ADE is a Java-based application that provides the interface for the selecting Argo temperature and salinity profiles from region of interest. In addition to the Argo data, value added products obtained from temperature and salinity profiles are also included. The interface provided in DVD gives the users power to select data from any region of interest, view the profile plots, zoom and filter based on multitude of queries. Users lacking high-speed network for downloading the Argo data, can order for a copy of the DVD.
Paper No
25
Publication ID : 314 & Year : 2010
Title
SONIC LAYER DEPTH VARIABILITY IN THE ARABIAN SEA
Authors
T. V. S Udaya Bhaskar, Debadatta Swain and M. Ravichandran
Source
Volume 4, Number 1,pp 17 - 28, International Journal of Oceans and Oceanography
Abstract
Spatial and temporal distribution of sonic layer depth (SLD) in the Arabian Sea (AS) was studied using temperature and salinity (T/S) profiles from Argo floats during the years 2003 2004 and World Ocean Atlas 2001 (WOA01) climatology. SLD was obtained from sound velocity profiles computed from T/S data. SLD variability as obtained from Argo matched well with those obtained from the WOA01 in certain locations and showed remarkable difference in some other. SLD variability in the AS is mainly related to seasonal variations in T/S owing to influence of seasonal phenomena as well as the geography of the region. Deeper SLDs were observed during summer monsoon (> 90 m) and winter monsoon (> 80 m) respectively. Up-welling and down-welling (Ekman dynamics) associated with the Findlater Jet controlled SLD during the summer monsoon. While in winter monsoon, cooling and convective mixing regulated SLD in the study region. Weak winds, high insolation and positive net heat flux lead to the formation of thin, warm and stratified sonic layer during pre and post summer monsoon periods, respectively. Examination of SLD in selected areas further revealed clear seasonal changes reflecting strong monsoon signals in the AS
Paper No
26
Publication ID : 306 & Year : 2009
Title
Web based Argo Data Services
Authors
E. Pattabhi Rama Rao, T.V.S. Uday Bhaskar, R. Devendar
Source
The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVIII-4-8/W14, Hyderabad 2009, pp. xx-xx.ISSN No:1682-1750.
Abstract
Argo is a global array of 3,000 profiling floats that measures temperature and salinity of the upper 2000 m of the ocean. Argo program began a new era in ocean observations by brining a sea of change in the way oceans are observed and data being made available for operational users and research community after real-time and delayed mode quality control. The abundance and real-time availability of the Argo data have lead to several new insights in oceanographic studies and enhanced significantly our understanding on the role of the ocean in climate change. Advances in information, communication and geospatial technologies enabled provision of web-based oceanographic data services. This paper describe in detail, how these technologies are utilized for providing web-based Argo data services. Web-based Argo data services facilitate users with Web-GIS capabilities to query, analyze, visualize and download the Argo data and products on user defined temporal and spatial domains. Brief account on generation of objectively analyzed monthly Argo data products and dissemination through our website is also discussed. Live Access Server (LAS) provides flexible access to geo-referenced scientific data using OpenDAP and DODS technology. Efforts in promoting open standards and interoperability activities for seamless exchange of ocean and atmospheric data in gridded format through Live Access Server (LAS) is discussed. INCOIS-LAS is a promising web application for serving the gridded Argo data and products. This can be used for on-the-fly visualization of data with user defined spatial and temporal subsets, request custom subsets of variables in a choice of file formats, access to metadata, comparison of variables from distributed locations and download the data using a simple graphical user interface.
Paper No
27
Publication ID : 161 & Year : 2009
Title
Comparison of AMSR-E and TMI sea surface temperature with Argo near surface temperature over the Indian Ocean
Authors
Udaya Bhaskar, T.V.S., Rahman, S.H., Pavan, I.D., Ravichandran, M., Nayak, S
Source
International Journal of Remote Sensing, Vol 30 Issue 3,PP 2669 2684
Abstract
Sea surface temperature (SST) derived from Advanced Microwave Scanning
Radiometer for Earth Observing System (AMSR-E) and Tropical Rainfall Measuring
Mission (TRMM) Microwave Imager (TMI) are compared with near surface
temperature (foundation-SST) in situ measurements obtained from Argo floats over
Indian Ocean. Spatial variation has been compared for 2002-2006, whereas for
temporal variation collocated observations from 11 floats have been used. Results
show that TMI and AMSR-E SST measurements are slightly over estimated during
pre and post monsoon and underestimates during monsoon season. Statistical analysis
shows that SST from AMSR-E is found to be better correlated with Argo foundation-
SST compared to TMI. The standard deviations (SD) and root mean square error
(RMSE) for AMSR-E retrieved SST are 0.58 C and 0.35 C over the Equatorial
Indian Ocean (EIO). The corresponding values for TMI are 0.66 C and 0.47 C. Over
the Arabian Sea although SD values are slightly higher compared to EIO values,
RMSE values are less for both TMI and AMSR-E retrieved SSTs. These retrieval
accuracies are above expected retrieval accuracy. Seasonal average spatial distribution
of AMSR-E SST show better match with the Argo foundation-SST compared to TMI
SST distributions. Robustness of the good spatial match during monsoon season may
be attributed due to the strong wind.
Paper No
28
Publication ID : 307 & Year : 2009
Title
A Web-GIS Interface for an Integrated In-situ Ocean-Data and Information System
Authors
R Venkat Shesu, E Pattabhi Rama Rao, TVS Udaya Bhaskar
Source
The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVIII-4-8/W14. Hyderabad 2009, pp. xx-xx. ISSN No:1682-1750
Abstract
The present study focuses on the Web Map Service (WMS), which is being integrated with the vector data available in the in-situ oceanographic data at the Indian National Centre for Ocean Information Services (INCOIS). In this paper, we describe our efforts to implement GIS services according to Open Geospatial Consortium (OGC) standard specifications. Through the use of Web Services, the integration of GIS services with the operational services like information and data management is discussed. WMS enables the creation of Web maps that have layers coming from multiple different remote servers/sources/platforms, which are used to integrate data from heterogeneous in-situ platforms, enabling easy access to end users.
Paper No
29
Publication ID : 163 & Year : 2008
Title
Seasonal variability of Sonic Layer depth in the central Arabian Sea.
The seasonal variability of the sonic layer depth in the central AS (0 to 25N and 62 66E) was studied using the temperature and salinity (T/S) profiles from Argo floats for the year 2002 2006. The atmospheric forcing responsible for the observed changes was explored using the meteorological data from NCEP/NCAR and Quickscat winds. Sonic layer depth (SLD) was obtained from sound velocity profiles computed from T/S data. SLD in the central AS was regulated by the net heat flux and wind forcing. Upwelling and downwelling (Ekman dynamics) associated with the Findlater Jet controlled the sonic layer depth during the summer monsoon. While in winter the cooling and convective mixing regulated SLD. Weak winds, high sea surface temperature, high positive net heat flux, lead to the formation of thin, warm and stratified sonic layer during pre and post monsoon periods respectively
Paper No
30
Publication ID : 164 & Year : 2007
Title
Mixed layer variability in the Northern Arabian Sea as detected by an Argo Float.
Seasonal evolution of surface mixed layer in the Northern Arabian Sea (NAS) between 17 N 20.5 N and 59 E 69 E was observed by using an Argo float daily data for about 9 months, from April 2002 through December 2002. Results showed that during April May mixed layer shoaled due to light winds, clear sky and intense solar insolation. Sea surface temperature (SST) rose by 2.34 C and ocean gained an average of 99.8 Wm-2. Mixed layer reached maximum depth of about 71 m during June - September owing to strong winds, cloudy skies. Ocean gained abnormally low ~ 18 Wm-2 and SST dropped by 3.41 C. During the inter monsoon period, October, mixed layer shoaled and maintained a depth of 20 to 30 m. November December was accompanied by moderate winds, dropping of SST by 1.5 C and ocean lost an average of 52.5 Wm-2. Mixed layer deepened gradually reaching a maximum of 62 m in December. Analysis of surface fluxes and wind, suggested that wind is the dominating factor causing deep mixed layer during summer monsoon periods and fluxes are dominant factor responsible for deep mixed layer due to convective mixing during winter monsoon period.
Paper No
31
Publication ID : 166 & Year : 2006
Title
Inferring mixed-layer depth variability from Argo observation in the western Indian Ocean.
Authors
Udaya Bhaskar, T.V.S., Swain, D., Ravichandran, M
Source
Journal of Marine Research, Volume 64, PP 393-406
Abstract
The seasonal and spatial variability of mixed layer depth (MLD) was examined in the Western Indian Ocean (300E 800E and 100S 300N) for three consecutive years starting from June 2002 May 2005 using Argo temperature and salinity (T/S) profiles. These were compared with MLD estimates from World Ocean Atlas 2001 (WOA01) T/S data. Temporal and spatial variability of MLD estimated from Argo T/S profiles were found to correspond well with the MLD obtained from WOA01 T/S data in the study area with slight deviations in the form of months of occurrence of minima and maxima MLDs. Argo MLD under estimated WOA01 MLD from January June and over estimated from July December for the three years of study (2002 2005). It is also observed that MLD variability features as brought out by both the data sets followed the dynamics that govern the mixed layer in this region of study.
