6.2 EVALUATION BY USER-REQUIREMENT CRITERIA
0 0 0 0 3 1
17 6 1 245
10 2 64
296
125
36 42
9 0 8 7 0 0
0 0 0 0 3 1
16
5 1 2 3 0
35 141
9 2
27 36 8
0 5 4 0 0 0
0 50 100 150 200 250 300
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Hour of day (GMT)
Number of alerts
Preoperational and operational season Operational season only
Figure 14. Number of possible fires (AVHRR) per hour of daytime detected by 'FireAlarm' system in the year 2000 (until 24 July).
In the case of AVHRR-scenes, the maximum number of potential fires (group of high intensity pixels) per scene reaches its maximum at 13.00 - 14.00 GMT; the rate is high already at 12.00 - 13.00 GMT but the number of available scenes is smaller.
For the time after 14.00 GMT the number of potential fires reduces again, although there are more scenes available. Up until evening the number of potential fires diminish further, but we can see also here a correlation with the number of available scenes. If we look at the morning hours, there is a maximum of potential fires at 06.00 - 07.00GMT for AVHRR and 09.00 - 10.00 GMT for ATSR- data.
The scenes are influenced by the character or the quality of the scenes, e.g. the available swath width and nadir or off-nadir view for AVHRR, or the observed area in ATSR-scenes. The most important time when the 'FireAlarm' system can observe active fires is covered by the first afternoon overpass of a NOAA-satellite. There is also a considerable number of fires during the hours before. This time is only partly covered by ERS-2.
In general, the requested alarm time of 0.5 hours from the start of the fire, as cited in user requirement R6 in Table 3, can not be reached due to the revisit rate of the satellites. The short alarm time would require the inclusion of a large number of satellites in the observation. Since the main focus is towards sparsely populated areas, or areas where no other infrastructure for alarming is given, the present revisit times still provide a valuable improvement to the previous fire management systems.
6.2.2 Size of detected fires
In 1999, a total of 1212 forest fires have been reported in Finland, burning 550 ha of forest. The average size per fire is 0.45 ha. The size distribution of reported fires is shown in Figure 15.
Reported fires in 1999
902
143
78 59
19 5 5 0
0 100 200 300 400 500 600 700 800 900 1000
<0.1 0.1-0.5 0.5-1 1-3 3-6 6-10 10-50 >50
Size (ha)
Number of fires
Figure 15. Forest fires reported by the authorities in Finland during the period of 10.4.1999 to 28.11.1999 (accidents only, no prescribed burnings).
During the period from 5.5.1999 to 4.10.1999, the prototype fire detection system that operated before the 'FireAlarm' system detected and sent alerts for about 68 possible fires (c.f. Figure 16).
0 0
1
6
7
6
14
0 0
2 4 6 8 10 12 14 16
<0.1 0.1-0.5 0.5-1 1-3 3-6 6-10 10-50 >50
Size (ha)
Number of fires
Figure 16. Fire alerts issued for Finland by the prototype fire detection system before the 'FireAlarm' system during the period 5.5.1999 to 22.9.1999
Direct estimate of the proportion of fires detected by 'FireAlarm' system is impossible based on the data of 1999. The major part of fires detected by the 'FireAlarm' system were prescribed burnings, which are absent from the list of reported fires. The technical implementation of the 'FireAlarm' system and the satellite constellation have restrictions on the fire detection performance, such as minimum detectable fire size. Additional detailed field data about fires is needed before any comprehensive analysis.
The known sizes of detected forest fires in 1999 were always larger than 1 ha, and most of them were prescribed burnings (the requirement is 0.1 ha). On the other hand, rather small fires of a house burning and a fire in a wooden factory (size of 200 m2) or at a landfill site have been detected. Also, in case of straw fires, the active burning area usually remains rather small, but many of them have been detected using satellite images.
This shows that also smaller sizes are visible if the fire is intense enough. One reason why a small fire has not been detected is that most of the fires are ground fires that are covered by a canopy layer.
Therefore the signal is too weak in comparison to the pixel size of the satellite image. They still have an influence on the signal, but it is difficult to discriminate fires from other radiation sources like hot soil or from clouds. Furthermore, small fires generally have only a short active period. Therefore, it is likely that they are not active during a satellite overpass.
According to Briess [1994], fires with a low temperature, T = 500 K, smouldering and open burning fires with T = 800 K, and fires smaller than 1% of the pixel size are hard to discriminate from reflections from water surfaces or clouds.
6.2.3 False alarm rate
In 1999, 11 out of 110 verified fires were false alarms, which meets the user requirement R7 (c.f.
Table 3) of 10%. 7 of these 11 false alarms were due to bit errors in the raw satellite images, caused by data transmission errors from NOAA-satellites.
NOAA-15, which in 1999 was less than 1 year old, was most affected by reception errors and missing data. Bit errors - and false alarms due to bit errors - were present also in the data from
‘good’ satellites.
In summer 1999, the prototype fire detection system was used. Detection of image lines that are affected by bit errors relied only on the 6-word synchronisation sequence at the beginning of each line (and a time code). A more complete screening for bit errors (see section 5.4.1) was implemented in the 'FireAlarm' system used in summer 2000.
Beside the false alarms caused by bit errors in 1999, there were also four cases of false alarms, which could not be explained despite interactive checking of the satellite scenes. These cases were close to clouds (but not in clouds) that could be thunder clouds.
Another technical problem comparable to the bit error problem of 1999 surfaced in May 2000. On 16th May 2000, a calibration error occurred in a NOAA-14 scene, causing 68 false alarms. The reason is that during the calibration of the instrument a hot source had been in the field of view while the instrument was supposed to look into space. After that, the software was upgraded to take this type of calibration error into account.
A source of false alarms that cannot be eliminated is industrial sites. When a new industrial site that exposes heat-emitting surfaces to open air begins to operate, it is typically detected as a fire. These can then be eliminated as industrial sites from the processing of later scenes if a verification fax is received from the fire authorities. This requires frequent checking of the response faxes.
6.2.4 Geo-location accuracy of detected fires
The user requirement (R8 in Table 3) for the location accuracy of detected fires is 500 m. The location accuracy is very crucial for fire brigades to save time in driving to the right place.
The forest fire detection processing excludes industrial sites as false alarms. All ‘fires’ within a defined radius (20 km for AVHRR, see Table 6) from known industrial sites are screened out as false alarms. The location data of these ‘fires’ (like that of any other fires or false alarms) is kept in a log file produced by the system. As far as it can be assumed that the heat source in these industrial sites (mainly steel factories) is always in the same place, the observations of the industrial targets can be used to estimate the geo-location accuracy of detected fires.
Figure 17 shows the dispersion of the observations of the Lulea industrial site in a graphical form.
There are 10 ATSR observations (the first on 7th December 1999, the last on 27th April 2000) and 15 AVHRR observations (the first on 22nd April 2000, the last on 15th July 2000). The small number of observations is due to the clouds and the irregularity of the operation of the factory. Even in cloud-free conditions, the factory does not always expose hot surfaces to the satellite sensors.
The lack of ATSR observations after 27th April 2000 is because the day-time fire detection threshold was above the sensor saturation limit in the 3.7-µm data.
The AVHRR observations in Figure 17 are derived from scenes where the geo-location accuracy has been improved by using automatic (image correlation) ground control points (GCP’s). The ATSR observations rely directly on the geo-location data that are supplied with the scenes. These data have been computed at the receiving station in Tromso using predicted orbital data of the ERS- 2 satellite. Even though the observations come from the same industrial site with a limited geographic area, it may be that the actual heat source (e.g. some hot material cooling in an open area) has been in a slightly different position during the image acquisition times corresponding to different observations. Change in the heat source position could also be the reason for the slight difference in the average target co-ordinates between the sensors. ATSR observations are mainly from winter time while the AVHRR observations are from summer time. It should be noticed that these industrial sites are not visible in each scene, which could also refer to a discontinuous nature of the source.
Figure 17. Dispersion of the observations of the Lulea industrial site. Green = ATSR, Red
= AVHRR. The line in blue is the boundary of the industrial site as derived from a 1:50000 topographic map.
The standard deviation of the location of the industrial site is higher than the nominal spatial resolution of the sensor (1.1 km for NOAA AVHRR). The actual spatial resolution of the AVHRR sensor degrades towards the edges of image swath (where the pixel size is 5.8 x 2.2 km), which makes accurate geo-location difficult unless the fire is in the very central part of the scene.
6.2.5 Alarming time- time delay caused by data acquisition
The alarming time is the time span between the ignition of the fire and the reception of the alert in the dispatching centre. Within the 'FireAlarm' system, only the time spent for the data processing and sending the alert can be influenced. The main part of the time from fire ignition to the reception of the
satellite data depends on the orbit constellation and cannot be changed. Furthermore, the fire has to grow first to a size that it is possible to be detected.
AVHRR data are received in real time during the data acquisition. ATSR data are recorded in the mass memory onboard the satellite. These data are then played back when the satellite is over the receiving station at Tromsö. Morning data (08.00 ... 10.00 GMT in the monitoring area) are acquired in descending orbits and stored onboard the satellite for almost one full orbit (about 100 minutes). The evening data (18.00 ... 20.00 GMT in the monitoring area) are acquired in ascending orbits and stored onboard the satellite for only 5 ... 10 minutes.
The alarming time is defined to start at the moment when the fire is ignited. Since this moment is usually unknown, alarming time is not a very useful quantity to measure the performance of a fire detection system. We define the ‘technical alarming time’ to be the time from the beginning of image acquisition until a fire report is received at a regional dispatching centre.
The technical alarming time is within 30 min for AVHRR data. The technical alarming time can be divided into the following components:
• receiving the scene (12...15 minutes)
• polling interval of 7 minutes (which could be reduced)
• the time of mirroring the scene from the receiving station
• the processing time at FMI computers (on ukko.fmi.fi 4...6 minutes)
• sending of faxes (of the order of 5 minutes).
The list shows that the processing time itself is only a minor part of the technical alarming time. Most of the technical alarming time is determined by various data services. Sending of telefax fire reports is done using a commercial fax-sending service (the so-called FaxPlus service operated by the telecom operator Sonera). The PostScript program that describes the fax is sent to the FaxPlus service by e-mail. After the fax has been sent, the FaxPlus service responds by sending an acknowledgement e-mail.
Figure 18 shows the histogram of the technical alarming time (from the start of receiving the data until fax transmission) in the pre-operational period in May-July 2000. The technical alarming time has been computed as the difference between the time stamp of the acknowledgement e-mail from the FaxPlus service and the time code of the first line in the scene where the fire was detected.
Most of the faxes were sent in less than 30 minutes from the beginning of image acquisition. The average technical alarming time was about 26.6 minutes. The outliers in Figure 18 around 57 minutes are three faxes stemming from a single NOAA AVHRR scene. The processing of this scene was blocked by the receiving station because two acquisitions followed each other in a too short period. The processing of the first scene was not finished before the beginning of the reception of the
second scene. Excluding this and two other similar outliers, the average technical alarming time was 25.2 minutes.
0 2 4 6 8 10 12 14
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57
Time since beginnining of acquisition (min)
# faxes
Figure 18. Histogram of technical alarming time (in minutes) in the period from 17.05.2000 to 24.07.2000.
The time needed for sending the alert can be reduced (possibly by 5 minutes) in the future by an electronic alert message.
6.2.6 User satisfaction
The fire alerts are sent to the dispatching centres, where the information about a possible fire is evaluated and redistributed to the corresponding fire brigade - unless the fire is already under attention or unless it is a prescribed burning. So far the dispatching centres represent the user of the system. To get quantification the dispatchers were asked to rank the system according to location accuracy, information content, reliability and the auxiliary information provided on the Internet.
Answers were received from 17 out of 36 dispatching centres. Not all of these have received a fax alert sent from the 'FireAlarm' system, and some received only one. The result of the quantification after averaging is as follows (Table 11) :
Table 11. User satisfaction in Finland
1. Location of the fire 2.5 1= bad, 5= excellent
2. Information given by the fax alert 2.9 1= bad, 5= excellent 3 Reliability of the alert 2.8 1= bad, 5 excellent 4. Information provided on the internet 2.6 1= bad, 5= excellent
Overall 2.7
The answers referred mostly to the alert time, where the fax alert is received after the first alerts of the fires have already been issued. The second most mentioned point refers to the location of the fire and its map representation. The accuracy should be improved and its location should be shown on a more detailed map to have a better idea of the location. Currently the fax map shows an area of approximately 400 km by 280 km. Also the fact that a fax alert is received even in the case when a fire is located in the neighbouring region can cause irritation. Also the local time should be shown, when indicating the fire on the map.
Several answers refer to the reliability, which should be improved in the future. Furthermore, an integration of the alert system into the electronic system has been considered useful. This would also allow a more detailed graphical representation, and it would not rely on the fax connection, which the responses have shown as not always being available.
Answers referring to the Internet pages mentioned the language, which is English and the use of abbreviations. The actual fire map shown on the Internet should allow further information about a particular fire. Such a system could be similar to the lightning representation from FMI on the Internet.
6.2.7 Application by other users outside Finland 6.2.7.1 Northern Europe
For the observation of forest fires a co-operation exists with the autonomous republic Carelia in Russia and with Estonia, Latvia, Norway, and Sweden. When sending fax alerts to several authorities it has to be taken into account that other alarming systems also exist. It is possible that additional difficulties arise due to the language, especially when working with east European countries, since English has not been the common working language in the past. The number of
responses to the fax alerts was shown in Table 9. In the year 2000, responses have been received from all the included countries so far.
In Finland the alert message is sent directly to the alarming centre, but to other countries the alert is sent via a central authority of the country, from where the message has to be redistributed. The answer is handled in the reverse way, what could also explain a delay or lack of responses.
The information itself is also somewhat different. Whereas in Finland a local co-ordinate system is used to indicate the location, other countries use geographic co-ordinates. It might be also useful in the future to only use the local language. This requires additional work from the local authorities.
The cyrillic font used in Russian could also be a problem in sending (PostScript) faxes.
Since the detection time is given in GMT, the local time of image recording might be given as well, to give a better overview or to avoid irritations.
Although the north south extension of the observation area is large, all countries and regions included in this project are situated in the boreal region and the natural conditions, such as temperature and vegetation, are more or less similar. This allows the application of a general set of threshold values for fire detection. These threshold values are selected according to the experience acquired over several seasons. Extending the fire detection system towards regions south of the Baltic republics would require a modification of the fire detection thresholds.
6.2.7.2 Southern Europe
Constraints on adaptation of the application to Southern Europe are similar to the ones in Northern Europe. Different definitions of forest exist in Mediterranean countries, as well as different methods to collect information.
In addition, new thresholds for fire detection would need to established, and new databases need to be generated (e.g., existing industrial sites).
6.2.8 Fire risk assessment by fire index
The assessment of forest fire risk in Finland uses an estimate of surface moisture as a measure of fire risk. The method is physically realistic and simple enough for public use. The forest fire warning consists of public announcements of the fire warning and an Internet service directed to fire officials providing information of the fire risk index. The 'FireAlarm' system has connected the forest fire alert and the fire index on the web-pages, from where this information is available to the users.
Fire index values are calculated on a 10 km by 10 km grid, which ensures that the spatial variation of the index is well taken into account. Also, the temporal variation of the index is accurate as the index is based on volumetric soil surface moisture.
The index is calibrated to the conditions of boreal forests and the method could be used in the whole boreal zone that covers northern Europe, large parts of Siberia and North America. Similar conditions can be found also at mountainous regions at lower latitudes in places with coniferous forest. To be able to calculate the index, precipitation and potential evaporation values are needed.
When compared with fire indices used in other countries the current method is a very modern system. It takes into account the important meteorological parameters as well as the weather conditions during the previous days and weeks. The underlying concept of the method is universal, i.e. the estimation of surface moisture, and thus the adaptation of the method to another country or region is a relatively easy task.
NOAA AVHRR can be used to determine vegetation stress. A system providing such information at the EU level is currently available at JRC. The 'FireAlarm' system could be easily modified to include forest fire risk evaluation. However, it should be noted that the vegetation stress index should be calibrated for Finland before it is used. This calibration-validation would be carried out with the use of fire statistics.
Currently, there is a tool available that provides an overview of wildfires in large areas of the world.
This is the Global Fire Web (http://www.ruf.uni-freiburg.de/fireglobe/) maintained by the Global Fire Monitoring Center, which is an activity of the UN International Strategy for Disaster Reduction.
However, the products integrated in the Global Fire Web have in many cases not been validated.
6.3 SUPPORTING INFORMATION ON FIRE SUSCEPTIBILITY, FUEL AMOUNT,