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总括与议论

时间:2022-01-26 百科知识 版权反馈
【摘要】:现在有的系统既在切断发射电流时,又在通电时测量二次场,这是时间域航空电磁法观测方法的一个飞跃式进步。
总括与议论_重磁与时间域电磁

10.4 总括与议论

10.4.1 总括

(1)无论固定翼飞机TDEM系统,还是直升飞机TDEM系统,发射磁矩都很大,基本频率降低并可调,而且发射电流采用方波波形,因此系统频带很宽。另外,由于其采集、存储、处理(数字)数据的能力有了很大的提高,可记录叠加之前的大量数据,经过适当的处理,信噪比提高很多,因此系统的探测深度可达500m左右,有的业者说还能探测得更深。

(2)在INPUT等系统中,为了避免干扰,一般在切断发射电流的情况下(offtime)测量二次场。现在有的系统既在切断发射电流时,又在通电时(ontime)测量二次场,这是时间域航空电磁法观测方法的一个飞跃式进步。利用数字一次场补偿算法,可将测得的数据转换成标准一次场波形激励下二次场的数据,进而计算并绘制导电率深度图,用作地质解释。

(3)以往只测量Rx、dB/dt,现在测量多分量x、y、z,不仅测量dB/dt,而且还测量B(由dB/dt得来或利用SQUID和fluxgate实测),测量吊舱(“bird”或吊架、吊框)的位置变化,使解释更准确,可根据直升飞机EM探测结果直接钻探,直升机TDEM方法可望代替地面EM方法。有的地球物理学家设想为将来的系统取名EXTREM,其特点是:低速、宽带、大功率、三维,多个基本频率,全时段数据(on timeoff time),接收机与发射回线固定在一起(x、y、z三个线圈,x、y、z三个SQUIDs),或者置于吊舱中(也是x、y、z三个线圈,x、y、z三个SQUIDs),现在有的厂家已在研发[37]

(4)IP方法是很有效的找矿方法,但是地面IP工作效率低。现在时间域航空EM已触及到了激发极化现象,当然还需要深入研究[38~39]。频率域EM方法也可能触及到激发极化现象,要用很低的频率,观察电阻率随测量频率的变化。通过不断地研究,EM和IP两种方法有可能衔接起来。

(5)应用范围广泛,可用于普查矿产、浅层油气、地下水,进行地质填图、风化层填图、盐碱地调查,进行工程基础调查,寻找UXO等[10]

10.4.2 议论

作者认为,航空磁测、航空重力测量和航空电磁测量(特别是时间域电磁法系统)是地质调查、矿产普查和国土资源调查工作中的三个重要的手段。我国航空磁测应用广泛、成效很大、技术比较成熟,但与世界先进水平相比,还有很大的差距,仍需努力提高。应用于地球物理调查的航空重力测量,在我国基本上还是一片空白,亟待研究开发。至于航空电磁方法,无论时间域的还是频率域的,在我国都有了开端,频率域方法的工作做得更多一些。国际上航空电磁方法发展迅速,科学家们及时采用各个学科的最新成就,使航空电磁方法不断向前发展,测量方法、数据处理和解释方法日趋完善。关于时间域航空电磁法,我们看到,固定翼飞机飞得高,发射磁矩可以达到很大,适宜于在高原、高山地区进行大面积普查;直升飞机方案很多,发射磁矩也很大,适用于比较崎岖的地形,在局部地区进行探测,可代替地面工作,有利于环境保护。

我国地域辽阔,地质、地形、自然景观、地电条件、调查对象和目的有很大的差别,任务有轻重缓急。发展ATDEM要有全面的发展规划,全盘考虑长远、短期、目前;究竟是租赁、引进还是自主研制应该有明确的政策,作者认为应该自主开发研制和引进并举。自主开发研制可考虑分三步走:首先研究开发直升飞机TDEM系统,一个可以考虑的方案是将现有的地面TDEM系统经过改进升级,发展为直升飞机TDEM系统;其次研究开发中型飞机TDEM系统;最后预研大型飞机TDEM系统。

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