ERS SAR DATA APPLICATION USE FOR STUDYING SEA ICE PARAMETERS AND RETRIEVING OF GREENLAND SEALS MIGRATION Vladimir V. Melentyev (1), Lasse H. Pettersson (2), Vladimir I. Chernook (3) (1)
Nansen International Environmental and Remote Sensing Center Korpousnaya Str. 18, St. Petersburg, 197110, Russia E-mail: vladimir.melentyev@ niersc.spb.ru (2)
Nansen Environmental and Remote Sensing Center Edv. Griegsv. 3A, Bergen, N-5059, Norway E-mail:
[email protected]
(3)
Polar Research Institute of Marine Fisheries and Oceanography (PINRO) Knippovich Str. 18, Murmansk, 197110, Russia E-mail:
[email protected]
INTRODUCTION Airborne observations of the ocean in IR and visible range became now an indispensable part of fish industry. An application of satellite data to studying the number of population of sea mammals has been attractive for biologists for a long period. However, the practical use of satellite information to study the behavior of sea mammals was restrained by its small spatial resolution. Additional limits were connected with the daytime illumination and cloud influence in Arctic. After the launching ERS synthetic aperture radar, which provides the all-weather sounding and fine spatial resolution, the situation has changed [1-3]. The vitality of this study is confirmed by the fact, that satellite radar information is the main and sometimes the only source for sea ice and other objects studies in the Polar region. Using ERS SAR signatures of the ice as non-biotic factor of ecology of Pagophillus groenladicus and others seals is a new approach in marine biology” [2, 3]. The White Sea as Barents and Pechora Seas are the inhabited areas of harp seals and the first experience of this kind of SAR application study was received by NERSC/NIERSC and PINRO in February-March 1997, when under-satellite observations of seas migration were organized onboard nuclear icebreaker “Taymir”[1,2]. The continuation of this study was done in 1998 - 2000 winter seasons in the framework of national and international fund, including A03.440 Project. Aircraft PINRO Antonov-26 and helicopter were used to carry out under-satellite experiments. SPECIFIC OBJECTIVES • •
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Studing and classification of radar signatures of different environmental objects (open water, sea and brackish-water ice, snow cover, coastal zones and water catchment) Monitoring of water masses arrangement, assessment of water catchment influence (including climatic aspect) Studying of ice dynamics and Barents-White Sea water exchange (ice drift as tracer of weather conditions and winter hydrology) Retrieving of ice parameters and harp seals migration study (ice as non-biotic factor of the White Sea population of Greenland seals)
METHODOLOGICAL ASPECTS, INSTRUMENTS AND DATA BASE In frame of this study more than 30 ERS SAR and RADARSAT images are used, part of them is received in near-real time. The composite ice maps based on SAR and other information were prepared. Archive SSMI daily scenes were available also. Separate scenes of visual and infrared satellite data for cloudless surveys were used.
The thematic decoding of satellite information was done with using airborne and in situ data. As it has been proved the position and displacement of ice massif that is selected by seals for whelping patches can fixed by SAR accurately [2-3]. Ice edge position was determined by using visual and passive microwave data (NOAA/DMSP) also. Possibilities of contouring of ice cover extension, dividing of fast ice and pack ice zones in the White Sea are the large advantages of ERS SAR surveys. It improves the organizing of the airborne reconnaissance of mammals essentially because harp seals avoid the fast ice zone for whelping. Comprehensive analysis of SAR and airborne data fixed that signature of floes that are selected by seals for whelping has contrast with the surrounding ice areas. The elicited fact is used as methodological approach for the thematic decoding of SAR data and for retrieving of the migration features. Short-period scenes are used for ice drift assessment. Long-term SAR series are used for determination of a connection between whelping patches location and annual modification of hydrological features, weather conditions and ice dynamic in central and southern parts of the White Sea (so-called “Basin” and “Neck”). Specific decoding indicators (radar signatures) of ice cover at the regions of mass congestion of sea mammals are retrieved from SAR satellite data and verified by aircraft and in situ observations. The aim was to reveal the contrasts of signatures of saline and brackish water ice. Variation of salinity of ice at different parts and gulfs of the White Sea, formation of level lubricious ice zones, regional features of snow parameters, arrangement of fractures and other opening in the ice are studied from point of view of the formation of different solidity of floes. ERS SAR signatures for the areas of mass congestion of seals are compared with pack ice zones that are avoided by seals as unfit (or uncomfortable) for whelping. The weather conditions which were studied in frame of this Project are characterizing the years with the different severity: 1998/99-winter at the north-north-western part of Russia was severe, 1999/2000 – anomaly warm. Ice drift and migration tendency at the different weather and ice conditions was detected with using SAR series. As was fixed by ERS data those hard frosts in 1998/99-winter season resulted in ice covering practically whole water area of the White Sea at the first stage of whelping (end of Februarybeginning of March). Another parameters retrieved from satellite SAR are the total and partial concentration of ice. Thematic decoding of SAR demonstrated that floe size as very important feature of ice for selecting of rookeries can be evaluated from SAR also. Small floes (20-100 m diameter) as ice cake and small ice cake zones has the bright contract. Harp seals avoided these. SAR data fixed compactness of pack ice in spring 1999 was extremely close creating the problems to mammals to penetrate deep into massif. This implies mammals need select for whelping the ice floes along the outward edges of the “Basin”, using the recurring cracks and opening in the ice here. The important stage of this study was detecting of ice drift vectors. Ice dynamics retrieved by SAR allow determining that adverse N/NE winds blocked up pack ice (and harp seals) inside the “Basin” till the end of April’99. According to [4], enclosing of the direction of traditional migration to the Barents Sea should provide destruction number of population (pups especially). Ecological catastrophe and following mass death of the White Sea population of Greenland seals as result of difficult environment and hostile ice conditions in 1999 was confirmed by marine biologists afterwards. Mass loss number of pup was fixed in March-April by helicopter. The research vessel NWPI met adults in summer season in unusual regions. Opportunity to predict by SAR the ecological catastrophe is the achievement of this information. 1999/2000 winter was anomaly warm in Russia, similar situations happened eight times at the 120years period of meteorological observations in RF. February and March monthly averaged air temperatures in Arkhangelsk exceeded the norm + 4 and + 3oC, correspondingly. According to in situ data, thin ice sufficient for organizing of whelping rookeries began forming at the third decade of February only, when air temperatures at the region fall several times till – 40oC. As result, ice-free conditions dominated at the main part of the White Sea in March-April. At this situation to find the rookeries without satellite data especially difficult. Determination by SAR ice floes convenient for whelping and monitor the tendency of ice drifts were the another tasks of this study. Field experiments’99 were organized at the “Neck”, Dvina and Mezen Bays (March-April), at Dvina Bay and Solovky Archipelago (June), at the “Neck”, Dvina, Chekh, Pechora and Khaypudirskaya Bays (September-October). 16 ERS SAR images were ordered and used in 1999 in frame A03.440. Field campaign’2000 was organized at the “Neck”, Dvina and Mezen Bay. It was studied also the incoming stream of Barents Sea waters along the Kola Peninsula (Murmansky Coast). 4 ERS SAR images were used in 2000 in frame A03.440. 4 ERS SAR extra-images were ordered by PINRO. These images were received in near real time, it were verified and used as the principal document for ice patrol and reconnaissance of whelping patches. 4 test-flights were done in March. Visual and IR airborne data are used for computation number of population. Multi-spectral information allows
avoiding the influence of daytime (shadows) and weather conditions (false heat targets), helps increasing accuracy in the count the harp seals (including taxation of adults and pups, separately). ICE PARAMETERS AND HARP SEALS MIGRATION FEATURES RETRIEVED BY ERS SAR
Fig. 1. 4 March 1999 ERS SAR data (2 scenes) 4 March 1999 08.41.27-08.41.57 ERS SAR data analysis (4 scenes) in connection with the initial stage of whelping – Fig. 1. Area observed: White Sea (Dvina Bay, northeastern part of “Basin”, “Neck”) and water catchment area (Onegsky, Zimny and Tersky Coasts). As SAR data fixes weather and ice conditions were favorable for whelping rookeries organizing at the end of February-beginning of March’99; when large part of fast ice zone at Dvina Bay was broken by eastern winds and displaced westward. Thin first-year (FY) ice dominated at the observed area. Eastern winds opened Dvina Bay and considerable part of “Neck” close to the Zimny Coast. Wind and Zimnegorsky stable current fractured ice cover along the outward borders of «Basin». Ice floes more suitable for whelping were located close to northeastern part of “Basin”. Such type of ice (thicker and fresher level ice area) has the dark signatures. Compacted ice edge (bright signature) restricted this area to mammals. According to SAR, ice situation became especially friendly for seals 2-4 March, when winds turned to the south. Southern winds were strong. Ice massif was pressurized additionally, additional braking of ice happened, including giant floes. These winds opened the fractures between eastern border of “Neck” and fast ice zone displaced from the western part of Dvina Bay. Southern winds which blown from mainland were cold and polynya at the “Neck” and Dvina Bay that was covered by new ice (slush) became frozen. Southern winds retrieved from SAR were propitious for ice drift toward to the Barents Sea and favorable for migration of mammals to the North. The general conclusion: 4 March 1999 harp seals should be located along to outward borders of «Basin» and at the southern part of the “Neck”.
Fig. 2. 17 March 1999 ERS SAR image (1 scene) 17 March 1999 08.32.25-08.33.10 ERS SAR data analysis (4 scenes) in connection with the first stage of whelping – Fig. 2. Area observed: White Sea (Mezen Bay, northeastern part of the «Neck», northwestern «entrance» to the sea) and surrounding regions (Kanin, Zimny and Abramov Coasts, Barents Sea). SAR fixes great number showings unsatisfactory conditions for seal migration. On our conclusion, vast dark frozen polynya close to the Kanin Coast was opened by NE winds 7-10 days ago. At the time of SAR survey it was covered by level gray-white ice. It means that this “opening” happened idem date. It means also that anti-cyclone with northward winds prevailed here whole mentioned period. As result of domination of this type of atmospheric circulation, sea mammals were “closed” in the White Sea. 17 March’99 SAR marked continuation of unfavorable conditions: ice drift southward could be marked as bright white traces behind the floes. Ice concentration evaluated as 9-10 tenths; thin fragmented FY ice dominated at the observed area. Giant ice floes was thin ice transient into medium. N/NE winds that blown at the time of SAR observations has the speed of 7-8 m/s. It ruffled the small water area at the Mezen Bay (as at the observed part of the Barents Sea). Freezing of the fractures happened at the different parts of sea. ERS SAR fixed this phenomenon as brightening of signal. It means that air temperatures should be evaluated minus 10-12oC. Zimniberezny stable current trace was pressed to the eastern part of “Neck”. Manifestation of this ice was marked as consecution of dark and gray zone elongated from SE to NW. The general conclusion: 17 March 1999 sea mammals still located at the southern part of «Neck». 20 March 1999 08.38.10-08.38.55 ERS SAR data analysis (4 scenes) in connection with the last stage of whelping – Fig. 3.
Fig. 3. 20 March 1999 ERS SAR image (1 scene)
Area observed: the White Sea (Mezen Bay, the «Neck» and «Funnel») and surrounding regions (Murmansky, Tersky and Zimny Coasts). As SAR data fixes weather and ice conditions continued to be extremely unfavorable for harp seals migration to the Barents Sea. N/NE winds continued to blow and hindered the ice drift to the Barents Sea. Ice concentration should be evaluated as 9-10 tenths; thin FY ice is dominated. Winds at the time of SAR observations were so strong that even giant ice floes was broken. Polynya along the Kanin Peninsula was broken also. Several separate ice floes at the SW border of mentioned above polynya were recognized and marked at 17 and 20 March SAR scenes. It used for the assessment of the wind speed and direction. For example, the floe that had coordinates of 67o10’N/42oE changed the position to 67oN/41o50’E. It means that ice drift was directed to the SSW. As can be retrieved from SAR, these winds stimulated additionally the opposite ice drifts at the whole water area from the «Funnel» to the «Neck» and far to the «Basin». The distance of 3-days drift was 25-30km. Ice drift to the south disturbed the migration features and continued to «close» the mammals inside the southern part of the observed area. Ice braking and fracturing resulted in the loss of rookeries, heavy casualties of pups. Air temperatures should be evaluated as minus 10-15oC, and following freezing of fractures is predicted. SAR detects opening in the ice and rafting processes as manifestations of tide. The general conclusion: regions of mass accumulation of seals were located 20 March 1999 at the central and southern parts of «Neck». Ice conditions that were reconstructed by SAR allow to suppose the opportunity of mass lost of harp seals at the second decade of March, and forecast the reducing of population and ecological catastrophe of the White Sea population of harp seals in 1999. 5 April 1999 08.35.19-08.36.55 ERS SAR data analysis (4 scenes) in connection with the final stage of harp seals migration within the bounds of White Sea – Fig. 4. Area observed: the White Sea («Funnel», Mezen Bay, northern part of «Neck») and surrounding regions (Kanin, Abramov and Zimny Coasts). 5 April is the date outside of the time of harp seals whelping migration within the White Sea traditionally. At this time the most part of White Sea became ice-free ice commonly, and ice floes with the one-month from birth generation reach to the southern limits of Barents Sea and mammals-reproducers complete the moulting in general. As SAR data fixes ice conditions were extremely unfavorable for seals at the end of March – beginning of April 1999. Almost whole-observed area was covered by ice, ice concentration should be evaluated as close to 10 tenths and freezing processes continued. NE winds that blow at the time of SAR observations is weak (2-3 m/s) and ice thickness development is evident from SAR data. Fast-ice zone was formed along the Kanin Coast (gray/gray-white ice). Ice began covering polynyas along the Tersky Coast; even the entrance of the Barents Sea waters nearby Cape Svyatoy Nos became frozen (dark nilas). That means air temperatures should be evaluated as minus 20oC. Different types of first-year ice are determined, but thin and thin transient into medium FY ice dominated at the whole observed water area. Ice cover got very fragmented, not numerous large floes keep only along the main stream of Zimnegorsky stable current (dark signatures). Analysis of radar signatures of river and lake ice demonstrates that the melting processes didn’t start at the White Sea region at first decade of April’99. N/NE winds that prevailed in March-April’99 hardly disturbed all features of harp seals migration; the
Fig. 4. 5 April 1999 ERS SAR image (1 scene)
Fig. 5. 20 March 2000 ERS SAR image (1 scene) direction and duration of each stage of seals migration was changed by hostile environment, mammals were «closed» inside the White Sea. The general conclusion: 5 April 1999 harp seals are still closed at the different parts of the White Sea, sea mammals lost the possibility to reach Barents region that was the main goal of pups migration. Mass destruction of mammals and reducing of population, ecological catastrophe of harp seals in 1999 is evident from the ice conditions retrieved by satellite radar. This conclusion was confirmed at the time of field experiments that were organized at the White Sea region by PINRO/NWRI in following spring –summer seasons . 20 March 2000 08.35.39-08.35.54 ERS SAR data analysis (2 scenes) in connection with inter-annual variability of seals migration tendency – Fig. 5. Area observed: the White Sea («Funnel», Mezen Bay, N/NE parts of «Neck») and surrounding regions (Zimny, Tersky and Abramov Coasts). Comprehensive analysis of satellite and in situ data demonstrates that ice conditions in 1999/2000winter season were unfavorable for whelping at first but the strong frosts at the third decade of February saved the situation. Fig. 5 (as 13, 17 March 2000 SAR data) fixes the large contrast of ice conditions for the period under review with the previous 1998/99 winter: partial ice covering with thin FY ice domination. According to SAR, ice parameters at the end of winter’2000 were quite suitable for whelping in White Sea. But at the time of SAR survey the situation wind was strong, it changed the direction from S/SE to the west. As result, the ice massif that was located along the Tersky Coast and pressed by S/SE winds, it began to move eastward. This situation got unfavorable for passive drift of
Fig. 6. Scheme of aircraft PINRO Antonov-26 harp seals reconnaissance, White Sea, 19 March 2000
Fig. 7 a,b. Ice zones convenient (a) and inconvenient (b) for whelping rookeries, that has the contrast of SAR signatures (dark and bright white area, correspondingly). Airborne photo survey, White Sea, 19 March 2000 ice to the Barents Sea for a certain time. The general conclusion: at the second decade of March’2000 mass rookeries of seals should be located close to the Tersky Coast. In frame of the concerned SAR scene, this area is fixed at the left lower corner of scene. It is marked as sufficiently long elongated dark zone nearby Sosnovka settlement. Harp seals mass accumulation area was separated from the another relatively thick ice zone along the ice edge at the “Neck” by incoming flux of Barents Sea’s stable current. The additional brightening of ice area close to centrum of “Neck” arised from the windy effects, discharging of ice and roughness of water surface in fractures. SAR validation program at the White Sea and surrounding waters was organized onboard aircraft PINRO Antonov-26. Multi-spectral (visual and IR) survey of ice cover parameters and harp seal was done 13, 15, 18 and 19 March 2000. Fig. 6 demonstrates the results of under-satellite ice observations and taxation number of population and migration tendency 19 March 2000. SAR prediction of rookery location was confirmed by airborne ice patrol. Airborne observations confirmed our conclusion about the contrast of signatures ice areas of mass rookeries and zones that are avoided by seals. The first is the level thick brackish water ice originated from relatively desalinated water masses, the second composed of ice cake and small floes is unfit for seals (Figure 7 a, b). These types of ice have the dark and white signature, correspondingly. CONCLUSIONS •
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ERS SAR data comprehensive analysis was done, radar signatures of ice at the different stages of harp seal migration in the White Sea were studied. It is proved that arrangement of the whelping rookeries of the Greenland seals close related on certain types of water masses, types and forms of drifting ice. Combine analysis of satellite, airborne and in situ data confirmed that SAR can be applied as instrument for seals migration monitor with using ice as non-biotic factor. Combine use of satellite and airborne data allows establish a connection the number of population with atmospheric circulation and ice type arrangement. Was concluded that ice conditions at White Sea in March-April 1999 were unfavorable for seals migration from the White to the Barents Sea. Ice floes that were used by sea mammals for the reproducing of posterity «were closed» at the «Basin» and south part of the «Neck». As result, reduction the number of population and following ecological catastrophe was predicted with using SAR. Airborne control surveys confirmed this forecast.
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Seasonal and annual modification of ice parameters were retrieved. Ice regime features and harp seals migration tendency in the White Sea in 1999/2000-winter season are studied by SAR and verified in frame of field campaign. The perspectives of harp seals monitor in Arctic are connected with ENVISAT. Spaceborne SAR in combination with airborne survey is more prospective instrument for being made world-wide service of sea mammals tomorrow. As our preliminary study show, satellite SAR can be used for control of the migration features for other representatives of seals in Arctic (including Jan-Majen and Newfoundland population of Greenland seals, and hooded seals also).
ACNOWLEGEMENTS The authors would like to thank Dr Kjell T. Nielsen from Norvegian Institute of Fishery and Aquaculture (Tromse, Norway) for helpful discussion the perspectives of SAR application use in marine biology and studying the seals migration at the different marginal seas in Arctic by SAR. We thank the people from ERS Help and Order Desk and Dr. Andrea Bellini personally for their supplying of the operational use of SAR data. This work is supported by ESA, 20 ERS SAR images of the White Sea and region were obtained in frame A03.440 Project. REFERENCES [1] O.M. Johannessen, S. Sandven, L.H. Pettersson, M. Miles, V.V. Melentyev, L.P. Bobylev. “Northern Sea Route Ice Monitoring by Satellite Radar Data,” Proc. of the 16th Int. Conference on Offshore Mechanics and Arctic Engineering. H. Yamagushi Eds. Book No. HO 1083, pp. 9-17, 1997. [2] V.I. Chernook, O.M. Johannessen, V.V. Melentyev. “Connection between Distribution of Harp Seals and Ice Cover Parameters Determined Using ERS-2 SAR Imagery,” Proc. of the ICES/NAFO Workshop on Survey Methodology for Harp and Hooded Seals. Copenhagen, 28.08-02.09.97, pp. 2227, 1997. [3] V.V. Melentyev, V.I. Chernook, O.M. Johannessen “Analysis of Ice Dynamics of Arctic Seas for Research of the Harp Seals Migration in the White Sea Using Satellite Data,” Earth Obs. Rem. Sens. No. 5, pp. 76-93, 1998 (in Russian). [4] “Hydrometeorology and hydrochemy of the Seas of USSR”. Vol. 2 “The White Sea”. 273p., 1991 (in Russian).
